Damper mechanism

ABSTRACT

A damper mechanism  6  is provided to transmit torque while absorbing and damping torsional vibrations. A small coil spring  45  achieves characteristics of a low rigidity in a small torsion angle region of the torsion characteristics when compressed by rotary members. A coil spring  33  achieves characteristics of a high rigidity in a large torsion angle region of the torsion characteristics when compressed by the rotary members rotating relatively to each other. A frictional resistance generating mechanism  7  generates a frictional resistance while each spring is being compressed. Owing to a rotating-direction space  79 , the frictional resistance generating mechanism  7  does not operate in the second stage of the torsion characteristics and also does not in the first stage while a torsion angle is in a predetermined range.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a damper mechanism.More specifically, the present invention relates to a damper mechanismfor transmitting a torque while absorbing and damping torsionalvibrations. The present invention also relates to a flywheel assembly,especially a flywheel assembly that is elastically coupled to acrankshaft in a rotational direction.

[0003] 2. Background Information

[0004] A clutch disk assembly used in a vehicle has a clutch functionfor releasably engaging a flywheel, and a damper function for absorbingand damping torsional vibrations transmitted from the flywheel. Ingeneral, vibrations of vehicles include idling noises (rattling noises)driving noises (acceleration and deceleration rattling noises andmuffled noises), and tip-in/tip-out (low-frequency vibrations). Forsuppressing such noises and vibrations, the clutch disk assembly isprovided with a damper.

[0005] The idling noises are rattling noises, which are generated from atransmission when a clutch pedal is released after shifting a gearposition to neutral, e.g., to stop at a traffic light. These noises aredue to the fact that an engine torque is low and varies to a largeextent in response to engine combustion when an engine speed is in ornear an idling range. In or near the idling range, tooth collisionsoccur between an input gear and a counter gear of the transmission.

[0006] The tip-in/tip-out (low frequency vibrations) is a largelongitudinal vibration of a vehicle body, which occurs when a driverrapidly depresses or releases an acceleration pedal. If a powertransmission system has a low rigidity, a torque transmitted to tires isreversely transmitted from the tires to the power transmission system.This reaction cause an excessive torque to be transmitted to the tiresso that large longitudinal vibrations transitionally occur to vibratethe vehicle body longitudinally to a large extent.

[0007] The idling noises are significantly affected by torsioncharacteristics of a clutch disk assembly at and around a zero torque,and can be effectively prevented by reducing a torsional rigidity at andaround the zero torque. Conversely, for reducing the longitudinalvibrations of the tip-in/tip-out, torsion characteristics of the clutchdisk assembly must be solid to a large extent.

[0008] For overcoming the above problems, a clutch disk assembly hasbeen provided that uses two kinds of spring members for providingcharacteristics having two stages. In this structure, the torsionalrigidity and a hysteresis torque are kept low in the first stage (lowtorsion angle region) of the torsion characteristics. This is effectivein preventing noises during idling. Since the torsional rigidity and thehysteresis torque are kept high in the second stage (high torsion anglerange) of the torsion characteristics, the longitudinal vibrations oftip-in/tip-out can be sufficiently damped.

[0009] Further, such a damper mechanism has been known that it caneffectively absorb minute torsional vibrations without operating a largefrictional resistance mechanism for the second stage when the minutetorsional vibrations are applied, e.g., due to combustion variations ofthe engine in the second stage of the torsion characteristics.

[0010] The damper mechanism described above can be achieved by providinga frictional resistance generating mechanism having the followingspecific structures. The frictional resistance generating mechanism isarranged as a whole to operate in parallel with a spring member of ahigh rigidity in a rotational direction, and has a frictional resistancegenerating portion, and a rotating-direction engagement portion arrangedto operate in series with respect to the frictional resistancegenerating portion in the rotational direction. The rotating-directionengagement portion has a minute rotating-direction space between twomembers.

[0011] In the prior art, the rotating-direction space can be configuredto operate in response to minute torsional vibrations only in the secondstage (large torsion angle region) of the torsion characteristics.

[0012] In some cases, however, vibration damping performance can beimproved, when such a manner is employed that a large frictionalresistance does not occur even when the torsion angle exceeds apredetermined angle in the first stage (small torsion angle region) ofthe torsion characteristics, and thus a large frictional resistance doesnot occur in response to the minute torsional vibrations.

[0013] Specifically, the damper mechanism described above is achieved byproviding a frictional resistance generating mechanism having thefollowing structure. This frictional resistance generating mechanism isarranged to operate in parallel with spring members, which have a highrigidity as a whole, in the rotating direction. Further, the frictionalresistance generating mechanism has a frictional resistance generatingportion and a rotating-direction engagement portion arranged to operatein series with respect to the frictional resistance generating portionin the rotating direction. The rotating-direction engagement portion isformed of a minute rotating-direction space between two members.

[0014] Accordingly, when minute torsional vibrations caused bycombustion variations of an engine aregenerated, the minuterotating-direction space prevents the operation of the frictionalresistance generating portion.

[0015] However, when torsional vibrations of a large torsion angle areapplied, the frictional resistance generating portion operates, and thefrictional resistance generating portion does not operate correspondingto the minute rotating-direction space only on the opposite sides, ofthe torsion angle range. Thus, a large frictional resistance suddenlyoccurs on the opposite sides of the torsion angle range when torsionalvibrations of a large torsion angle are applied. This large frictionalresistance increases the impact of collision between the members formingthe rotating-direction space so that hitting or tapping noises occur.

[0016] In conventional damper mechanisms, a flywheel is fixed to acrankshaft of an engine for absorbing vibrations caused by combustionvariations of the engine. Further, a clutch device is arranged on thetransmission side of the flywheel in an axial direction. The clutchdevice includes a clutch disk assembly coupled to an input shaft of atransmission and a clutch cover assembly for biasing a frictionalcoupling portion of the clutch disk assembly with the flywheel. Theclutch disk assembly has a damper mechanism for absorbing and dampingtorsional vibrations. The damper mechanism has elastic members such ascoil springs, which are disposed for compression in the rotatingdirection.

[0017] A structure is also known such that the damper mechanism isarranged not in the clutch disk assembly but between the flywheel andthe crankshaft. In this structure, the flywheel is located on an outputside of a vibration system, in which the coil springs provide a boundarybetween the output and input sides, and an inertia on the output side islarger than that in a conventional structure. Consequently, a resonancerotation speed can be set below an idling rotation speed and a highdamping performance can be achieved. The structure formed of the abovecombination of the flywheel and the damper mechanism provides theflywheel assembly or the flywheel damper.

[0018] When the flywheel assembly described above receives torquevariations from an engine, the springs in the damper mechanism arecompressed in the rotational direction to absorb and damp the torquevariations. Further, the damper mechanism has a frictional resistancegenerating mechanism formed of a plurality of members, therefore slidingoccurs in the frictional resistance generating mechanism to generate apredetermined hysteresis torque when springs are compressed.Consequently, torsional vibrations are rapidly damped.

[0019] The damper mechanism includes a pair of input plates opposed toeach other, an output plate disposed between the input plates, and acoil spring circumferentially and elastically coupling the pair of inputplates to the output plate. The pair of input plates is fixed togetherby a plurality of stop pins on the radially outer side so that the inputplates rotate together. The stop pins are inserted into recesses formedat an outer periphery of a flange. The pair of input plates can rotatethrough a predetermined angle range with respect to the flange, and therelative rotation stops when the stop pins come into contact with thecircumferential ends of the recesses. As described above, the stop pinscouple the pair of input plates together as well as function as astopper with respect to the flange.

[0020] The stop pin must have a certain diameter and must be disposedradially inside the outer periphery of the pair of input plates. Due tothese conditions, it is impossible to increase a relative rotation anglebetween the input plate pair and the flange in the structure employingthe stop pins. This means that the performance of coil springs cannot befully utilized even if the coil springs have a high strength because therelative rotation angle cannot be increased sufficiently. For reducingtooth-hitting noises and muffled noises of a drive system during drivingof a vehicle, it is necessary to minimize a torsional rigidity in anacceleration/deceleration torque range for setting a torsional resonancefrequency of the drive system to a value lower than an actual rotationrange. For achieving the low torsional rigidity and a further increasedstopper torque, it is necessary to ensure a wide torsion angle.

[0021] In view of the above, it will be apparent to those skilled in theart from this disclosure that there exists a need for an improved dampermechanism. This invention addresses this need in the art as well asother needs, which will become apparent to those skilled in the art fromthis disclosure.

SUMMARY OF THE INVENTION

[0022] An object of the present invention is to improve a torsionalvibration damping function by generating a predetermined frictionalresistance in both of first and second stages of the torsioncharacteristics of a damper mechanism while preventing generation of apredetermined frictional resistance in response to minute torsionalvibrations.

[0023] Another object of the present invention is to suppress occurrenceof hitting noises in a frictional resistance generating mechanism, whichis provided with a minute rotating-direction space for absorbing minutetorsional vibrations.

[0024] Still another object of the present invention is to overcome theproblem caused by conventional stop pins in a flywheel assembly, and toincrease sufficiently a relative torsion angle between the input andoutput members.

[0025] According to a first aspect of the present invention, a dampermechanism provided to transmit a torque while absorbing and dampingtorsional vibrations includes a first rotary member, a second rotarymember, a first elastic member, a second elastic member, a frictionalresistance generating mechanism, and a frictional resistance suppressingmechanism. The second rotary member is rotatable relative to the firstrotary member. The first elastic member is compressed in response torelative rotation between the first and second rotary members to achievelow rigidity characteristics in a small torsion angle region of thetorsion characteristics. The second elastic member is compressed inresponse to relative rotation between the first and second rotarymembers to high rigidity achieve characteristics in a large torsionangle region of the torsion characteristics. The frictional resistancegenerating mechanism generates a frictional resistance when the firstelastic member is in a compressed state and when the second elasticmember is in a compressed state. The frictional resistance suppressingmechanism has a rotating-direction space to prevent the frictionalresistance generating mechanism from operating in a predetermined anglerange.

[0026] According to this damper mechanism, when the first and secondrotary members rotate relatively to each other, the first and secondelastic members are compressed, and the frictional resistance generatingmechanism generates a frictional resistance. Consequently, the torsionalvibrations are rapidly absorbed and damped. In a small torsion angleregion, the first elastic member is compressed to achieve low-rigiditycharacteristics. In a large torsion angle region, the second elasticmember is compressed to achieve the high-rigidity characteristics. Inany region, the frictional resistance generating mechanism operates togenerate the frictional resistance. However, when minute torsionalvibrations are applied, the rotating-direction space of the frictionalresistance suppressing mechanism acts to stop or prevent the operationof the frictional resistance generating mechanism in any angle range.Thus, a large frictional resistance does not occur in response to theminute torsional vibrations in a first stage of the torsioncharacteristics, therefore, torsional vibration damping performanceimproves.

[0027] According to a second aspect of the present invention, the dampermechanism of the first aspect further has a feature such that thefrictional resistance generating mechanism and the frictional resistancesuppressing mechanism are arranged to operate in parallel with the firstand second elastic members in the rotational direction.

[0028] In this damper mechanism, since the frictional resistancegenerating mechanism and the frictional resistance suppressing mechanismare arranged to operate in parallel with the first and second elasticmembers in the rotational direction, these mechanisms are able tooperate when the first and second elastic members operate.

[0029] According to a third aspect, the damper mechanism of the secondaspect further has such a feature that the first and second elasticmembers operate in series in the rotational direction.

[0030] In this damper mechanism, the first and second elastic membersoperate in series in the rotational direction, however, the secondmember is hardly compressed when the first elastic member is beingcompressed.

[0031] According to a fourth aspect of the present invention, the dampermechanism of the first, second, or third aspect further has a featuresuch that the frictional resistance generating mechanism realizes firstregions for increasing stepwise a frictional resistance on oppositesides of a range of the predetermined angle, respectively, and a secondregion for providing a constant frictional resistance.

[0032] In this damper mechanism, the frictional resistance increasesstepwise in the first region before the large frictional resistance isgenerated in the second region. Thus, a wall of a high hysteresis torquedoes not exist when generating the large frictional resistance. Thisreduces hitting or tapping noises of claws, which may occur when thedamper mechanism generates a high hysteresis torque.

[0033] According to a fifth aspect of the present invention, the dampermechanism of the fourth aspect further has a feature such that thefrictional resistance generating mechanism generates an intermediatefrictional resistance in the first region.

[0034] In this damper mechanism, an intermediate frictional resistanceoccurs in the first region before a large frictional resistance occursin the second region. Thus, a wall of a high hysteresis torque does notexist when generating the large frictional resistance. This reduceshitting or tapping noises of claws, which may occur when the dampermechanism generates a high hysteresis torque.

[0035] According to a sixth aspect of the present invention, the dampermechanism of the fourth aspect further has a feature such that thefrictional resistance generating mechanism generates a frictionalresistance increasing smoothly in the first region.

[0036] In this damper mechanism, a frictional resistance increasingsmoothly occurs in the first region before a large frictional resistanceoccurs in the second region. Thus, a wall of a high hysteresis torquedoes not exist when generating the large frictional resistance. Thisreduces hitting or tapping noises of claws, which may occur when thedamper mechanism generates a high hysteresis torque.

[0037] According to a seventh aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst frictional resistance generating portion, a second frictionalresistance generating portion, a first frictional resistance suppressingportion, and a second frictional resistance suppressing portion. Thesecond frictional resistance generating portion generates a frictionalresistance larger than that generated by the first frictional resistancegenerating portion. The first frictional resistance suppressing portionhas a first rotating-direction space to prevent the operation of both ofthe first and second frictional resistance generating portions. Thesecond frictional resistance suppressing portion has a secondrotating-direction space to prevent the operation of only the secondfrictional resistance generating portion on the opposite sides of atorsion angle range of the first rotating-direction space.

[0038] In the frictional resistance generating mechanism, when thetorsion angle of the torsional vibrations is within the torsion anglerange of the first rotating-direction space in the first frictionalresistance suppressing portion, the first rotating-direction spaceprevents the operation of the first and second frictional resistancegenerating portions so that a large frictional resistance does notoccur. When the torsion angle of the torsional vibrations is within thetorsion angle range of the second rotating-direction space of the secondfrictional resistance generating portion, the second rotating-directionspace only permits the operation of the first frictional resistancesuppressing portion to generate a frictional resistance of anintermediate magnitude. When the torsion angle of the torsionalvibrations exceeds the torsion angle range of the secondrotating-direction space, the second frictional resistance generatingportion operates to generate the largest frictional resistance.

[0039] As described above, the first frictional resistance generatingportion generates frictional resistance of an intermediate magnitude inthe torsion angle range of the second rotating-direction engagementportion before the second frictional resistance generating portionoperates to generate the large frictional resistance. In this manner,the large frictional resistance rises in a multi-step or stepwisefashion so that a wall of a high hysteresis torque does not exist whenthe large frictional resistance is generated. Thereby, hitting ortapping noises of claws, which may occur when a high hysteresis torqueoccurs, can be reduced in the frictional resistance generatingmechanism.

[0040] According to an eighth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst frictional resistance generating portion and a second frictionalresistance generating portion. The first frictional resistancegenerating portion does not operate within a first torsion angle range,and operates in second torsion angle ranges provided on the oppositesides of the first torsion angle range, respectively. The secondfrictional resistance generating portion does not operate within thefirst and second torsion angle ranges, and operates on the oppositesides of the second torsion angle ranges.

[0041] In the frictional resistance generating mechanism, when thetorsion angle of the torsional vibrations is within the first torsionangle range, neither of the first and second frictional resistancegenerating portions operates, thus, a large frictional resistance doesnot occur. When the torsion angle of the torsional vibrations is withinthe second torsion angle range, only the first frictional resistancegenerating portion operates to generate a frictional resistance of anintermediate magnitude. When the torsion angle of the torsionalvibrations exceeds the second torsion angle range, the second frictionalresistance generating portion operates to generate the largestfrictional resistance.

[0042] As described above, the first frictional resistance generatingportion generates the frictional resistance of an intermediate magnitudewithin the second torsion angle range before the second frictionalresistance generating portion operates to generate the large frictionalresistance. In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when the large frictional resistance is generated.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0043] According to a ninth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes alarge frictional resistance generating mechanism, a large frictionalresistance generation suppressing mechanism, and a small frictionalresistance generating mechanism. The large frictional resistancegeneration suppressing mechanism has a rotating-direction space toprevent operation of the large frictional resistance generatingmechanism. The small frictional resistance generating mechanismgenerates a frictional resistance smaller than the frictional resistancegenerated by the large frictional resistance generating mechanism on theopposite sides of the rotating-direction space.

[0044] In the frictional resistance generating mechanism, when thetorsion angle is within the torsion angle range of an middle portion ofthe rotating-direction space, neither of the small and large frictionalresistance generating mechanisms operates, thus, a large frictionalresistance does not occur. When the torsion angle of the torsionalvibrations is within the torsion angle range of the opposite ends of therotating-direction space, only the small frictional resistancegenerating mechanism operates to generate a frictional resistance of anintermediate magnitude. When the torsion angle of the torsionalvibrations exceeds the torsion angle range of the rotating-directionspace, the large frictional resistance generating mechanism operates togenerate the largest frictional resistance.

[0045] As described above, the small frictional resistance generatingmechanism generates the frictional resistance of an intermediatemagnitude on the opposite ends of the torsion angle range of therotating-direction space before the large frictional resistancegenerating mechanism operates to generate the large frictionalresistance. In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when the large frictional resistance is generated.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0046] According to a tenth aspect of the present mechanism, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst friction portion and a second friction portion. The first frictionportion has a first hysteresis torque generating portion, and a firstrotating-direction space arranged to operate in series with respect tothe first hysteresis torque generating portion in a rotating direction.The second friction portion has a second hysteresis torque generatingportion and a second rotating-direction space. The second hysteresistorque generating portion is arranged in the rotating direction betweenthe first hysteresis torque generating portion and the firstrotating-direction space. The second hysteresis torque generatingportion generates a hysteresis torque smaller than the hysteresis torquegenerated by the first hysteresis torque generating portion. The secondrotating-direction space is arranged to operate in series with respectto the second hysteresis torque generating portion in the rotatingdirection.

[0047] In the frictional resistance generating mechanism, when thetorsion angle of the torsional vibrations is within the torsion anglerange of the first rotating-direction space of the first frictionportion, neither of the first and second hysteresis torque generatingportions operates, thus, a large frictional resistance does not occur.When the torsion angle of the torsional vibrations exceeds the torsionangle range of the first rotating-direction space of the first frictionportion to fall within a torsion angle range of the secondrotating-direction space of the second friction portion, the secondhysteresis torque generating portion operates to generate a hysteresistorque of an intermediate magnitude. When the torsion angle of thetorsional vibrations exceeds a torsion angle range of the secondrotating-direction space, the first hysteresis torque generating portionoperates to generate the largest frictional resistance.

[0048] As described above, the second hysteresis torque generatingportion generates the frictional resistance of an intermediate magnitudein the torsion angle ranges of the second rotating-direction on theopposite sides of the first rotating-direction space before the firsthysteresis torque generating portion operates to generate the largefrictional resistance. In this manner, the large frictional resistancerises in a multi-step or stepwise fashion so that a wall of a highhysteresis torque does not exist when the large frictional resistance isgenerated. Thereby, hitting or tapping noises of claws, which may occurwhen a high hysteresis torque occurs, can be reduced in the frictionalresistance generating mechanism.

[0049] According to an eleventh aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst friction generating portion, a second friction generating portion,a first rotating-direction space forming portion, and a secondrotating-direction space forming portion. The second friction generatingportion is arranged to operate in parallel with the first frictiongenerating portion in the rotating direction. The firstrotating-direction space forming portion prevents the operation of thefirst friction generating portion in an initial stage of a torsionangle. The second rotating-direction space forming portion prevents theoperation of the second friction generating portion up to apredetermined torsion angle when the first friction generating portionis operating.

[0050] In the frictional resistance generating mechanism, when relativerotation starts between the two members, the first rotating-directionspace forming portion initially prevents operation of both the first andsecond friction generating portions. When the torsion angle exceeds aninitial stage, the first friction generating portion starts theoperation to generate a predetermined frictional resistance. When apredetermined torsion angle is achieved, the second rotating-directionspace forming portion is closed, and the second friction generatingportion generates a predetermined frictional resistance. Thus, the firstand second friction generating portions operate in parallel in therotating-direction to generate a frictional resistance larger than thatgenerated only by the first friction generating portion.

[0051] As described above, only the first friction generating portionoperates to generate the frictional resistance of an intermediatemagnitude in the predetermined torsion angle range of the secondrotating-direction space forming portion before the first and secondfriction generating portions operate in parallel in the rotatingdirection to generate the large frictional resistance. In this manner,the large frictional resistance rises in a multi-step or stepwisefashion so that a wall of a high hysteresis torque does not exist whenthe large frictional resistance is generated. Thereby, hitting ortapping noises of claws, which may occur when a high hysteresis torqueoccurs, can be reduced in the frictional resistance generatingmechanism.

[0052] According to a twelfth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includesfirst, second, and third friction generating portions as well as first,second, and third rotating-direction space forming portions. The first,second, and third friction generating portions are arranged to operatein parallel with each other in a rotating direction between the firstand second rotary members. The first rotating-direction space formingportion prevents an operation of the first friction generating portionin an initial stage of a torsion angle. The second rotating-directionspace forming portion prevents the operation of the second frictiongenerating portion up to a predetermined torsion angle when the firstfriction generating portion operates. The third rotating-direction spaceforming portion prevents an operation of the third friction generatingportion until a predetermined torsion angle is achieved during theoperation of the second friction generating portion.

[0053] In the frictional resistance generating mechanism, when relativerotation starts between the two members, the first rotating-directionspace forming portion initially prevents the operations of all thefirst, second, and third friction generating portions. When the torsionangle exceeds an initial stage, the first friction generating portionstarts the operation to generate a predetermined frictional resistance.When a predetermined torsion angle is achieved, the secondrotating-direction space forming portion is closed, and the secondfriction generating portion generates a predetermined frictionalresistance. Thus, the first and second friction generating portionsoperate in parallel in the rotating-direction to generate a frictionalresistance larger than that generated only by the first frictiongenerating portion. When another predetermined torsion angle isachieved, the third rotating-direction space forming portion is closed,and the third friction generating portion generates a predeterminedfrictional resistance. Thus, the first, second, and third frictiongenerating portions operate in parallel in the rotating-direction togenerate a frictional resistance larger than that generated by the firstand second friction generating portions.

[0054] As described above, only the first friction generating portioninitially operates before the first, second, and third frictiongenerating portions operate in parallel in the rotating direction togenerate the large frictional resistance. Then, only the first andsecond friction generating portions operate so that a frictionalresistance of an intermediate magnitude is generated in a stepwisefashion. In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when the large frictional resistance is generated.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0055] According to a thirteenth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes aplurality of friction generating portions and a plurality ofrotating-direction space forming portions. The plurality of frictiongenerating portions is arranged between the first and second rotarymembers to operate in parallel with each other in the rotatingdirection. The plurality of rotating-direction space forming portionsdelays the operations of the plurality of friction portions to startsuccessively the operations of the respective friction portions.

[0056] In the frictional resistance generating mechanism, when relativerotation occurs between the two members, the plurality ofrotating-direction space forming portions successively starts theoperations of the plurality of friction portions. Thus, the number ofthe friction generating portions operating in parallel with each otherin the rotating direction increases stepwise. In this manner, the largefrictional resistance rises in a multi-step or stepwise fashion so thata wall of a high hysteresis torque does not exist when the largefrictional resistance is generated. Thereby, hitting or tapping noisesof claws, which may occur when a high hysteresis torque occurs, can bereduced in the frictional resistance generating mechanism.

[0057] According to a fourteenth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes alarge friction generating portion and an intermediate frictiongenerating portion. The intermediate friction generating portiongenerates an intermediate frictional resistance smaller than africtional resistance generated by the large frictional resistancegenerating portion just before the large friction generating portionstarts operating. The magnitude of the intermediate frictionalresistance may be constant, may change in a multi-step fashion or maychange gradually.

[0058] In the frictional resistance generating mechanism, when relativerotation occurs between the two members, the large friction generatingportion operates to generate a large frictional resistance immediatelyafter the intermediate friction generating portion operates to generatethe intermediate frictional resistance. In this manner, the largefrictional resistance rises in a multi-step or stepwise fashion so thata wall of a high hysteresis torque does not exist when the largefrictional resistance is generated. Thereby, hitting or tapping noisesof claws, which may occur when a high hysteresis torque occurs, can bereduced in the frictional resistance generating mechanism.

[0059] According to a fifteenth aspect of the present invention, aflywheel assembly to transmit a torque from a crankshaft of an engine,includes a flywheel, an elastic coupling mechanism and a plate-likecoupling portion. The flywheel has a friction surface. The elasticcoupling mechanism is a mechanism to couple elastically the flywheel andthe crankshaft in a rotational direction. The elastic coupling mechanismhas a pair of first disk-shaped members, a second disk-shaped member,and an elastic member. The first disk-shaped members are axially spacedfrom each other and fixed together. The second disk-shaped member isarranged between the pair of first disk-shaped members. The elasticmember is provided to couple elastically the pair of first disk-shapedmembers to the second disk-shaped member in the rotational direction.The plate-like coupling portion extends between outer peripheries of thepair of first disk-shaped members and couples the pair of firstdisk-shaped members together.

[0060] In this flywheel assembly, the plurality of elastic memberstransmits the torque between the first disk-shaped plate pair and thesecond disk-shaped plate. When relative rotation occurs between the pairof first disk-shaped plate pair and the second disk-shaped plate, theelastic members are compressed therebetween. A conventional stop pin iseliminated, and the plate-like coupling portion couples the firstdisk-shaped plate pair to the second disk-shaped plate. The plate-likecoupling portion is radially shorter than the conventional stop pin,therefore can be disposed in the radially outermost position of thesecond disk-shaped plate. Therefore, the plate-like coupling portiondoes not interfere with the elastic members so that a torsion angle of adamper mechanism can be sufficiently increased.

[0061] According to a sixteenth aspect of the present invention, theflywheel assembly of the fifteenth aspect further has a feature suchthat the plate-like coupling portions are arranged at a plurality ofcircumferentially shifted positions, respectively.

[0062] According to a seventeenth aspect of the present invention, theflywheel assembly of the fifteenth or sixteenth aspect further has afeature such that the plate-like coupling portion has main surfacesdirected radially inward and outward, respectively.

[0063] According to an eighteenth aspect of the present invention, theflywheel assembly of the fifteenth, sixteenth or seventeenth aspectfurther has a feature such that the plate-like coupling portion extendsintegrally from one of the pair of first disk-shaped members.

[0064] According to nineteenth aspect of the present invention, theflywheel assembly of any one of the fifteenth to eighteenth aspectsfurther has a feature such that the second disk-shaped member isprovided with a stop portion colliding in the rotational direction withthe disk-shaped member when a torsion angle between the firstdisk-shaped member pair and the second disk-shaped member increases.

[0065] According to a twentieth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst rotary member, a second rotary member, a first intermediatemember, and a second intermediate member. The second rotary member isrotatable relatively to the first rotary member. The first intermediatemember engages with the first rotary member via a firstrotating-direction space. The second intermediate member cooperates withthe first intermediate member to form an engagement portion engagingwith the first intermediate member via a second rotating-directionspace. The second intermediate member also cooperates with the firstintermediate member to form a first frictional resistance generatingportion slidably and frictionally engaging in the rotating directionwith the first intermediate member. Further, the second intermediatemember cooperates with the second rotary member to form a secondfrictional resistance generating portion slidably and frictionallyengaging in the rotating direction with the second rotary member togenerate a frictional resistance larger than a frictional resistancegenerated by the first frictional resistance generating portion.

[0066] In this frictional resistance generating mechanism, when thefirst rotary member rotates relatively to the second rotary member, thefirst rotating-direction space between the first rotary member and thefirst intermediate member initially decreases. In this operation,neither the first nor the second frictional resistance generatingportions generates a frictional resistance. When the firstrotating-direction space disappears, the first intermediate memberrotates together with the first rotary member, and rotates relatively tothe second intermediate member. In this relative rotation, the firstfrictional resistance generating portion generates a frictionalresistance, and at the same time, the second rotating-direction spacedecreases. When the second rotating-direction space disappears, thesecond intermediate member rotates together with the first intermediatemember, and rotates relatively to the second rotary member. In thisrelative rotation, the second frictional resistance generating portiongenerates a frictional resistance larger than that generated by thefirst frictional resistance generating portion.

[0067] Consequently, in the frictional resistance generating mechanism,when a torsion angle of torsional vibrations is in an angle range of thefirst rotating-direction space, the first rotating-direction spaceprevents the operation of the first and second frictional resistancegenerating portions so that a large frictional resistance does notoccur. When the torsion angle of torsional vibrations is in an anglerange of the second rotating-direction space, due to the secondrotating-direction space only the first frictional resistance generatingportion operates so that a frictional resistance of an intermediatemagnitude occurs. When the torsion angle of torsional vibrations exceedsthe angle range of the second rotating-direction space, the secondfrictional resistance generating portion operates to generate thelargest frictional resistance.

[0068] As described above, the first frictional resistance generatingportion generates the frictional resistance of an intermediate magnitudein the torsion angle range of the second rotating-direction space beforethe second frictional resistance generating portion operates to generatethe large frictional resistance. In this manner, the large frictionalresistance rises in a multi-step or stepwise fashion so that a wall of ahigh hysteresis torque does not exist when generating the largefrictional resistance. Thereby, hitting or tapping noises of claws,which may occur when a high hysteresis torque occurs, can be reduced inthe frictional resistance generating mechanism.

[0069] According to a twenty-first aspect of the present invention, thefrictional resistance generating mechanism of the twentieth aspectfurther has a feature such that the first rotating-direction space islarger than the second rotating-direction space.

[0070] According to a twenty-second aspect of the present invention, thefrictional resistance generating mechanism of the twentieth ortwenty-first aspect further has a feature such that the first and secondintermediate members are disk-shaped members axially overlapping andbeing in contact with each other.

[0071] According to a twenty-third aspect of the present invention, thefrictional resistance generating mechanism of the twenty-second aspectfurther has a feature such that the second intermediate member is formedof a pair of members each being in contact with one of axially oppositesides of the first intermediate member. Each of the pair of memberscooperates with the first intermediate member to form the firstfrictional resistance generating portion therebetween, and cooperateswith the second rotary member to form the second frictional resistancegenerating portion therebetween.

[0072] According to a twenty-fourth aspect of the present invention, thefrictional resistance generating mechanism of the twenty-second ortwenty-third aspect further has a feature such that the firstrotating-direction space is radially positioned in an area defined byaxially overlapping portions of the first and second intermediatemembers.

[0073] In this frictional resistance generating mechanism, the radialposition of the first rotating-direction space is not shifted radiallyoutward from the axially overlapping portions of the first and secondintermediate members so that the structure can be small in size.

[0074] According to a twenty-fifth aspect of the present invention, thefrictional resistance generating mechanism of the twenty-fourth aspectfurther has a feature such that the first rotary member has adisk-shaped portion axially overlapping the first intermediate member.The first rotating-direction space is formed between the firstintermediate member and the disk-shaped portion of the first rotarymember.

[0075] In this frictional resistance generating mechanism, the firstrotating-direction space is formed between the first intermediate memberand the disk-shaped portion of the first rotary member so that thestructure of the first rotating-direction space can be simple.Therefore, the accuracy of the first rotating-direction space isimproved.

[0076] According to a twenty-sixth aspect of the present invention, thefrictional resistance generating mechanism of the twenty-fifth aspectfurther has a feature such that one of the first intermediate member andthe disk-shaped portion of the first rotary member is provided with aspace extending in the rotating direction, and the other is providedwith a projected portion extending axially through the space to form thefirst rotating-direction space.

[0077] In this frictional resistance generating mechanism, since thefirst intermediate member and the disk-shaped portion of the firstrotary member are provided with the space and the projection, thestructure of the first rotating-direction space can be simple.Therefore, the accuracy of the first rotating-direction space isimproved.

[0078] According to a twenty-seventh aspect of the present invention,the frictional resistance generating mechanism of the twenty-sixthaspect further has a feature such that the space is formed in thedisk-shaped portion of the first rotary member. The first intermediatemember is formed of a pair of members arranged on axially opposite sidesof the disk-shaped portion, respectively. One of the pair of members hasthe projected portion, and is unrotatably engaged with the other of thepair of members via the projected portion.

[0079] According to a twenty-eighth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional resistance generating mechanism includes afirst rotary member, a second rotary member, a first intermediatemember, and a second intermediate member. The second rotary member isrotatable relatively to the first rotary member. The first intermediatemember engages with the first rotary member via a first space in therotating-direction, and cooperates with the second rotary member to forma first friction generating portion therebetween. The secondintermediate member is arranged between the first and second rotarymembers to operate with respect to the first intermediate member in arotating direction such that an end of the second intermediate memberand an end of the first intermediate member exert forces on each other,engages with the first intermediate member via a second space in therotating-direction, and cooperates with the second rotary member to forma second friction generating portion therebetween.

[0080] In this frictional resistance generating mechanism, when thefirst rotary member rotates relatively to the second rotary member, thefirst rotating-direction space between the first rotary member and thefirst intermediate member initially decreases. In this operation,neither the first nor the second friction generating portions generatesa frictional resistance. When the first rotating-direction spacedisappears, the first intermediate member rotates together with thefirst rotary member, and rotates relatively to the second intermediatemember. In this relative rotation, the first friction generating portiongenerates a frictional resistance, and at the same time, the secondrotating-direction space decreases. When the second rotating-directionspace disappears, the second intermediate member rotates together withthe first intermediate member, and rotates relatively to the secondrotary member. In this relative rotation, the first and second frictiongenerating portions operate in parallel in the rotating direction, andgenerate a frictional resistance larger than that generated only by thefirst friction generating portion.

[0081] In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when generating the large frictional resistance.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0082] According to a twenty-ninth aspect of the present invention, thefrictional resistance generating mechanism of the ninth aspect furtherhas a feature such that the frictional resistance generating mechanismfurther includes a third intermediate member arranged between the firstand second rotary members to operate with respect to the first andsecond intermediate members in the rotating direction such that an endof the third intermediate member and an end of the first and secondintermediate members exert forces on each other, engaging with thesecond intermediate member via a third rotating-direction space, andcooperating with the second rotary member to form a third frictiongenerating portion.

[0083] In this frictional resistance generating mechanism, when thefirst rotary member rotates relatively to the second rotary member, thefirst rotating-direction space between the first rotary member and thefirst intermediate member initially decreases. In this operation,neither the first nor the second friction generating portions generatesa frictional resistance. When the first rotating-direction space isclosed, the first intermediate member rotates together with the firstrotary member, and rotates relatively to the second intermediate member.In this relative rotation, the first friction generating portiongenerates a frictional resistance, and at the same time, the secondrotating-direction space decreases. When the second rotating-directionspace disappears, the second intermediate member rotates together withthe first intermediate member, and rotates relatively to the secondrotary member. In this relative rotation, the first and second frictiongenerating portions operate in parallel in the rotating direction, andgenerate a frictional resistance larger than that generated only by thefirst friction generating portion. When the third rotating-directionspace disappears, the third intermediate member rotates together withthe second intermediate member, and rotates relatively to the secondrotary member. In this relative rotation, the first, second, and thirdfriction generating portions operate in parallel in the rotatingdirection, and generate a frictional resistance larger than thatgenerated only by the first and second friction generating portions.

[0084] In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that hitting or tapping noises ofclaws, which may occur when a high hysteresis torque occurs, can bereduced in the frictional resistance generating mechanism.

[0085] According to a thirtieth aspect of the present invention, africtional resistance generating mechanism is arranged between tworelatively rotatable members of a rotary mechanism to generate africtional resistance in response to relative rotation that occursbetween the two members by torsional vibrations to damp the torsionalvibrations. The frictional generating mechanism includes a first rotarymember, a second rotary member, and a plurality of friction members. Thesecond rotary member is rotatable relatively to the first rotary member.The plurality of friction members is arranged in a rotating directionbetween the first and second rotary members, and each of the frictionmembers frictionally engages with the second rotary member. The frictionmembers engage in series with each other in the rotating direction via arotating-direction space such that an end of one exerts force on an endof the other.

[0086] In this frictional resistance generating mechanism, when thefirst rotary member rotates relatively to the second rotary member, theplurality of friction members are driven by the first rotary member toslide with respect to the second rotary member and to generate africtional resistance. In this operation, the respective frictionmembers are successively driven while being spaced from each other bythe rotating-direction spaces. Thus, the hysteresis torque increases ina stepwise fashion.

[0087] In this manner, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when generating the large frictional resistance.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0088] According to the frictional resistance generating mechanism ofthe invention, when a torsion angle of torsional vibrations is in anangle range of the first rotating-direction space, the firstrotating-direction space prevents the operation of the first and secondfrictional resistance generating portions so that a large frictionalresistance does not occur. When the torsion angle of torsionalvibrations is in an angle range of the second rotating-direction space,the second rotating-direction space operates only the first frictionalresistance generating portion so that a frictional resistance of anintermediate magnitude occurs. When the torsion angle of torsionalvibrations exceeds the angle range of the second rotating-directionspace, the second frictional resistance generating portion operates togenerate the largest frictional resistance.

[0089] As described above, the first frictional resistance generatingportion generates the frictional resistance of an intermediate magnitudein the torsion angle range of the second rotating-direction space beforethe second frictional resistance generating portion operates to generatethe large frictional resistance. In this manner, the large frictionalresistance rises in a multi-step or stepwise fashion so that a wall of ahigh hysteresis torque does not exist when generating the largefrictional resistance. Thereby, hitting or tapping noises of claws,which may occur when a high hysteresis torque occurs, can be reduced inthe frictional resistance generating mechanism.

[0090] These and other objects, features, aspects, and advantages of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Referring now to the attached drawings which form a part of thisoriginal disclosure:

[0092]FIG. 1 is a schematic cross-sectional view of a clutch device inaccordance with a preferred embodiment of the present invention;

[0093]FIG. 2 is an alternate schematic cross-sectional view of theclutch device;

[0094]FIG. 3 is an elevational view of a flywheel damper of the clutchdevice;

[0095]FIG. 4 is a fragmentary view showing, on an enlarged scale, astructure of the clutch device of FIG. 1, and particularly illustratinga plate coupling portion thereof;

[0096]FIG. 5 is a fragmentary view showing, on an enlarged scale, astructure of the clutch device of FIG. 1, and particularly illustratinga frictional resistance generating mechanism thereof;

[0097]FIG. 6 is a fragmentary view showing, on an enlarged scale, astructure of the clutch device of FIG. 2, and particularly illustratingan alternate view of the frictional resistance generating mechanism;

[0098]FIG. 7 is a rear elevational view of the flywheel damper,illustrating the frictional resistance generating mechanism;

[0099]FIG. 8 is an elevational view of a damper mechanism in a hubflange of the clutch device;

[0100]FIG. 9 is an elevational view of the damper mechanism in clutchand retaining plates of the clutch device;

[0101]FIG. 10 is an elevational view of a second spring seat of thedamper mechanism;

[0102]FIG. 11 is a side view of the second spring seat viewed in adirection of arrow XI in FIG. 10;

[0103]FIG. 12 is a plan view of the second spring seat viewed in adirection of arrow XII in FIG. 10;

[0104]FIG. 13 is a rear view of the second spring seat viewed in adirection of arrow XIII in FIG. 10;

[0105]FIG. 14 is an elevational view of a first spring seat of thedamper mechanism;

[0106]FIG. 15 is a side view of the first spring seat viewed in adirection of an arrow XV in FIG. 14;

[0107]FIG. 16 is a rear view of the first spring seat viewed in adirection of an arrow XVI in FIG. 15;

[0108]FIG. 17 is a cross-sectional view of the first spring seat takenalong line XVII-XVII in FIG. 16;

[0109]FIG. 18 is a fragmentary cross-sectional view illustrating theengagement between the second spring seat and the hub flange;

[0110]FIG. 19 is a fragmentary cross-sectional view illustratingengagement of the second spring seat with the clutch and retainingplates;

[0111]FIG. 20 is a view of a mechanical circuit diagram of the dampermechanism;

[0112]FIG. 21 is a view of a torsion characteristic diagram of thedamper mechanism;

[0113]FIG. 22 is a fragmentary cross-sectional view illustrating anoperation of a small coil spring of the damper mechanism;

[0114]FIG. 23 is a fragmentary cross-sectional view illustrating anoperation of the small coil spring;

[0115]FIG. 24 is a fragmentary elevational view illustrating anoperation of the frictional resistance generating mechanism;

[0116]FIG. 25 is a fragmentary elevational view illustrating anoperation of the frictional resistance generating mechanism;

[0117]FIG. 26 is a fragmentary elevational view illustrating anoperation of the frictional resistance generating mechanism;

[0118]FIG. 27 is a view of a diagram illustrating torsioncharacteristics of the damper mechanism;

[0119]FIG. 28 is a view of a diagram illustrating torsioncharacteristics of the damper mechanism;

[0120]FIG. 29 is a view of a diagram illustrating torsioncharacteristics of the damper mechanism;

[0121]FIG. 30 is a cross-sectional view illustrating a frictionalresistance generating mechanism in accordance with a second preferredembodiment of the present invention;

[0122]FIG. 31 is an alternate cross-sectional view illustrating thefrictional resistance generating mechanism of the second embodiment.

[0123]FIG. 32 is an elevational view a first high-friction-coefficientfriction washer of the frictional resistance generating mechanism of thesecond embodiment;

[0124]FIG. 33 is a rear elevational view of the firsthigh-friction-coefficient friction washer of the second embodiment;

[0125]FIG. 34 is an elevational view of a secondhigh-friction-coefficient friction washer of the frictional resistancegenerating mechanism of the second embodiment;

[0126]FIG. 35 is a rear fragmentary elevational view of the secondhigh-friction-coefficient friction washer of the second embodiment;

[0127]FIG. 36 is an elevational view of an input friction plate of thefrictional resistance generating mechanism of the second embodiment;

[0128]FIG. 37 is an elevational view of a bushing of the frictionalresistance generating mechanism of the second embodiment;

[0129]FIG. 38 is an elevational view of a first low-friction-coefficientfriction washer of the frictional resistance generating mechanism of thesecond embodiment;

[0130]FIG. 39 is a fragmentary plan view illustrating a structure of afirst rotating-direction engagement portion of the frictional resistancegenerating mechanism of the second embodiment;

[0131]FIG. 40 is a fragmentary elevational view illustrating structuresof the first and second rotating-direction engagement portions of thesecond embodiment;

[0132]FIG. 41 is a view of a mechanical circuit diagram of a dampermechanism of a clutch device in accordance with the second embodiment;

[0133]FIG. 42 is a view of a torsion characteristic diagram of thedamper mechanism of the second embodiment;

[0134]FIG. 43 is a view of a torsion characteristic diagram of thedamper mechanism of the second embodiment;

[0135]FIG. 44 is a view of a torsion characteristic diagram of thedamper mechanism of the second embodiment;

[0136]FIG. 45 is a view of a torsion characteristic diagram of thedamper mechanism of the second embodiment;

[0137]FIG. 46 is a schematic cross-sectional view of a frictionalresistance generating mechanism in accordance with a third preferredembodiment of the present invention;

[0138]FIG. 47 is an alternate schematic cross-sectional view of thefrictional resistance generating mechanism of the third embodiment;

[0139]FIG. 48 is a fragmentary elevational view illustrating a firstrotating-direction engagement portion of the frictional resistancegenerating mechanism of the third embodiment;

[0140]FIG. 49 is a fragmentary elevational view illustrating a secondrotating-direction engagement portion of the frictional resistancegenerating mechanism of the third embodiment;

[0141]FIG. 50 is a schematic cross-sectional view illustrating assemblyof the frictional resistance generating mechanism of the thirdembodiment;

[0142]FIG. 51 is a view of a mechanical circuit diagram of a dampermechanism of a clutch device in accordance with the third embodiment;

[0143]FIG. 52 is a view of a mechanical circuit diagram of a dampermechanism in accordance with a fourth preferred embodiment of thepresent invention;

[0144]FIG. 53 is a view of a torsion characteristic diagram of a dampermechanism of the fourth embodiment;

[0145]FIG. 54 is a view of a mechanical circuit diagram of a dampermechanism in accordance with a fifth preferred embodiment of the presentinvention;

[0146]FIG. 55 is a view of a torsion characteristic diagram of thedamper mechanism of the fifth embodiment;

[0147]FIG. 56 is a view of a torsion characteristic diagram of thedamper mechanism in accordance with a sixth preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0148] Selected embodiments of the present invention will now beexplained with reference to the drawings. It will be apparent to thoseskilled in the art from this disclosure that the following descriptionsof the embodiments of the present invention are provided forillustration only and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

[0149] First Embodiment

[0150] A clutch device 1 in accordance with a preferred embodiment ofthe present invention shown in FIGS. 1 and 2 is to couple providedreleasably torque between a crankshaft 2 on an engine side and an inputshaft 3 on an transmission side. The clutch device 1 is primarily formedof a first flywheel assembly 4, a second flywheel assembly 5, a clutchcover assembly 8, a clutch disk assembly 9, and a release device 10. Thefirst and second flywheel assemblies 4 and 5 are combined to form aflywheel damper 11, which includes a damper mechanism 6 and is describedlater.

[0151] In FIGS. 1 and 2, O-O indicates a rotation axis of the clutchdevice 1. An engine (not shown) is disposed on the left side in FIGS. 1and 2, and a transmission (not shown) is disposed on the right side. Infollowing description, the left side in FIGS. 1 and 2 will be referredto as the engine side, which is based on the axial direction, and theright side will be referred to the transmission side, which is based onthe axial direction. In FIG. 3, an arrow R1 indicates a drive side,i.e., forward side in the rotational direction, and an arrow R2indicates a reverse drive side (rearward side in the rotationaldirection).

[0152] First Flywheel Assembly

[0153] Referring to FIGS. 1 and 2, the first flywheel assembly 4 isfixed to an end of the crankshaft 2. The first flywheel assembly 4 is amember that ensures a large moment of inertia on the crankshaft side.The first flywheel assembly 4 is primarily formed of a disk-shapedmember 13, an annular member 14, and a support plate 39, which will bedescribed later. The disk-shaped member 13 has a radially inner endfixed to an end of the crankshaft 2 by a plurality of bolts 15. Thedisk-shaped member 13 has bolt insertion apertures 13 a locatedcorresponding to the bolts 15, respectively. Each bolt 15 is axiallyattached to the crankshaft 2 from the transmission side. The annularmember 14 has a relatively thick block-like form, and is axially fixedto the transmission side of the radially outer end of the disk-shapedmember 13. The radially outer end of the disk-shaped member 13 is weldedto the annular member 14. Further, a ring gear 17 for an engine starteris fixed to the outer peripheral surface of the annular member 14. Thefirst flywheel assembly 4 may be integrally formed.

[0154] A structure of the radially outer portion of the disk-shapedmember 13 will now be described in greater detail. As shown in FIG. 5,the radially outer portion of the disk-shaped member 13 has a flat form,having a friction member 19 fixed to its axial surface on thetransmission side. The friction member 19 is formed of a plurality ofarc-shaped members, and has an annular form as a whole. In a relativerotation suppressing mechanism 24, which will be described later, thefriction member 19 functions as a member for damping shock, which iscaused when the first and second flywheel assemblies 4 and 5 are coupledtogether. The friction member 19 also serves to stop rapidly therelative rotation in the coupling operation. The friction member 19 maybe fixed to a disk-shaped plate 22, which will be described later.

[0155] The disk-shaped member 13 is provided with a cylindrical portion20 at its outer periphery extending axially toward the transmission sideas shown in FIG. 5. The cylindrical portion 20 is supported by the innerperipheral surface of the annular member 14, and is provided with aplurality of recesses 20 a at its end. Each recess 20 a has apredetermined angular length in the rotational direction. It can bedeemed that each recess 20 a is defined by axial projection on thecylindrical portion 20.

[0156] Second Flywheel Assembly

[0157] The second flywheel assembly 5 is primarily formed of a flywheel21 with a friction surface, and the disk-shaped plate 22. The flywheel21 with the friction surface has an annular and disk-shaped form, and isaxially located on the transmission side with respect to the outerperipheral portion of the first flywheel assembly 4. The flywheel 21with the friction surface is provided with a first friction surface 21 aon its transmission side. The first friction surface 21 a is an annularand flat surface, and can be connected to the clutch disk assembly 9,which will be described later. The flywheel 21 with the friction surfaceis further provided with a second friction surface 21 b on its engineside in the axial direction. The second friction surface 21 b is anannular and flat surface, and functions as a frictional sliding surfaceof a frictional resistance generating mechanism 7, which will bedescribed later. As compared with the first friction surface 21 a, thesecond friction surface 21 b has a slightly smaller outer diameter and asignificantly larger inner diameter. Accordingly, the second frictionsurface 21 b has a larger effective radius than the first frictionsurface 21 a. The second friction surface 21 b is axially opposed to thefriction member 19.

[0158] Description will now be given on the disk-shaped plate 22. Asseen in FIG. 2, the disk-shaped plate 22 is disposed axially between thefirst flywheel assembly 4 and the flywheel 21 having the frictionsurface. The disk-shaped plate 22 has a radially outer portion fixed toa radially outer portion of the flywheel 21 having the friction surfaceby a plurality of rivets 23, and functions as a member rotationaltogether with the flywheel 21 having the friction surface. Morespecifically, as seen in FIG. 5, the disk-shaped plate 22 is formed of aradially outer fixing portion 25, a radially outer cylindrical portion26, a contact portion 27, and a radially inner cylindrical portion 28,which are aligned radially in this order. The radially outer fixedportion 25 is flat and is in axial contact with the surface on theengine side of the radially outer portion of the flywheel 21 having thefriction surface. The radially outer fixing portion 25 is fixed to theradially outer portion of the flywheel 21 by the rivets 23 alreadydescribed. The cylindrical portion 26 extends axially toward the enginefrom the inner periphery of the radially outer fixed portion 25. Thecylindrical portion 26 is located radially inside the cylindricalportion 20 of the disk-shaped member 13. The cylindrical portion 26 isprovided with a plurality of recesses 26 a. Each recess 26 a is formedcorresponding to the recess 20 a in the cylindrical portion 20. Thecontact portion 27 has a circular and flat form, and corresponds to thefriction member 19. The contact portion 27 is axially opposed to thesecond friction surface 21 b of the flywheel 21 having the frictionsurface with a space therebetween. Various members of the frictionalresistance generating mechanism 7 to be described later are arranged inthis space. The frictional resistance generating mechanism 7 is disposedbetween the contact portion 27 of the disk-shaped plate 22 of the secondflywheel assembly 5 and the flywheel 21 having the friction surface sothat the required space of the structure can be small. The radiallyinner cylindrical portion 28 extends axially toward the transmission,and has an end neighboring the flywheel 21 having the friction surface.The radially inner cylindrical portion 28 is provided with an outerperipheral surface 28 a at its base portion, which is larger in diameterthan an outer peripheral surface 28 b on its tip end portion, and astepped portion is formed between these surfaces 28 a and 28 b.

[0159] As seen in FIGS. 1 and 2, the support plate 39 of the firstflywheel assembly 4 is a member to support radially the second flywheelassembly 5 with respect to the first flywheel assembly 4. The supportplate 39 is formed of a disk-shaped portion 39 a and a cylindricalportion 39 b extending axially from its inner periphery toward thetransmission. The disk-shaped portion 39 a is disposed axially betweenthe end surface of the crankshaft 2 and the disk-shaped member 13. Thedisk-shaped portion 39 a is provided with bolt insertion apertures 39 ccorresponding to the bolt insertion apertures 13 a, respectively. Owingto the above structure, the support plate 39 is fixed to the crankshaft2 by the bolts 15 together with the disk-shaped member 13 and an inputdisk-shaped plate 32.

[0160] An inner peripheral surface of the flywheel 21 with the frictionsurface is supported by the outer peripheral surface of the cylindricalportion 39 b of the support plate 39 via a bushing 47. In this manner,the support plate 39 centers the flywheel 21 having the friction surfacewith respect to the first flywheel assembly 4 and the crankshaft 2.

[0161] Damper Mechanism

[0162] Description will now be given on the damper mechanism 6. Thedamper mechanism 6 is a mechanism to couple elastically the crankshaft 2with the flywheel 21 having the friction surface in the rotationaldirection. The damper mechanism 6 is formed of a high-rigidity damper38, which includes a plurality of coil springs 33, and the frictionalresistance generating mechanism 7. The damper mechanism 6 furtherincludes a low-rigidity damper 37 for exhibiting low-rigiditycharacteristics in a region of a small torsion angle. Further, as shownin FIG. 20, the low- and high-rigidity dampers 37 and 38 are disposed tooperate in series in the rotational direction, and to operate inparallel with the frictional resistance generating mechanism 7 in therotational direction in the torque transmission system.

[0163] Referring again to FIGS. 1 and 2, a pair of output disk-shapedplates (30 and 31) is formed of a first plate 30 axially arranged on theengine side and a second plate 31 axially arranged on the transmissionside. These plates 30 and 31 have disk-shaped forms respectively, andare axially spaced by a predetermined distance from each other. Each ofplates 30 and 31 is provided with a plurality of spaced windows 30 a or31 a in the circumferential direction. The windows 30 a and 31 a areconfigured to support the coil springs 33, which will be describedlater, in the axial and rotational directions. Each window 20 a and 31 ahas a cut and bent portion, which axially holds the coil spring 33 andis in contact with circumferentially opposite ends thereof. As shown inFIG. 9, each of the windows 30 a and 31 a is defined by a pair of endsurfaces 94, which are located on the opposite ends in the rotationaldirection respectively, as well as a radially outer support portion 95and a radially inner support portion 96. Each end surface 94 and theradially inner support portion 96 extend substantially straight in theradial direction and the tangential direction respectively. The radiallyouter support portion 95 extends along an arc in the rotationaldirection.

[0164] A structure of the second plate 31 will now be described ingreater detail with reference to FIGS. 1 and 2. A disk-shaped body ofthe second plate 31 is provided with four circumferentially spacedwindows 31 a, and is also provided with rivet apertures 69 for rivets68, each of which is located between circumferentially neighboringwindows 31 a, as will be described later. As shown in FIGS. 3 and 4, thedisk-shaped body of the second plate 31 is provided with a plurality ofplate coupling portions 40 at its outer periphery extending axiallytoward the engine, i.e., toward the first plate 30. The plate couplingportion 40 is formed of an axially extending portion 41 and a fixedportion 42 extending radially inward from the end of the extendingportion 41. The end of the extending portion 41 is substantially locatedradially outside or parallel to the first plate 30. The extendingportion 41 has main surfaces directed radially inward and outwardrespectively, and thus has a radial width equal to the thickness of theplate 31. The fixed portion 42 is in contact with the side surface ofthe first plate 30 on the axial transmission side, and is fixed theretoby rivets 68. In this manner, the plates 30 and 31 are fixed togetherfor rotation together, and an intended axial space is maintainedtherebetween.

[0165] The input disk-shaped plate 32 is a disk-shaped member, disposedbetween the plates 30 and 31. The input disk-shaped plate 32 has aplurality of window apertures 32 a each extending in the circumferentialdirection, and the coil spring 33 and a small coil spring 45 arearranged within the window aperture 32 a. As shown in FIG. 8, the windowaperture 32 a is formed of a pair of end surfaces 91, which are locatedon the opposite ends in the rotational direction, respectively, as wellas a radially outer support portion 92 and a radially inner supportportion 93. Each end surface 91 extends substantially straight in theradial direction. Each of the radially outer support portion 92 and theradially inner support portion 93 extends along an arc in the rotationaldirection. The input disk-shaped plate 32 is provided with recesses 32b, each of which is located circumferentially between the neighboringwindow apertures 32 a to allow the rivet 68 to pass axiallytherethrough, as will be described later. As shown in FIGS. 3 and 4, theinput disk-shaped plate 32 is provided with contact portions 32 c, eachof which is spaced in the rotational direction from the extendingportion 41 but can come into contact with the extending portion 41.According to the above structure, the plate coupling portions 40 and thecontact portions 32 c form a stop mechanism in the damper mechanism 6 ofthis embodiment. However, the stop mechanism may be formed of portionsother than the above.

[0166] Each coil spring 33 is formed of a combination of large and smallsprings. Each coil spring 33 is arranged within the corresponding windowaperture 32 a and windows 30 a and 31 a, and is supported at itsopposite sides in the radial direction as well as at its opposite sidesin the rotational direction. Each coil spring 33 is also supported atits opposite sides in the axial direction within the windows 30 a and 31a.

[0167] Then, description will be given on a coupling structure 34 tocouple the output disk-shaped plates 30 and 31 with the flywheel 21having the friction surface. The coupling structure 34 is formed ofbolts 35 and nuts 36. The second plate 31 is provided with a pluralityof fixed portions 31 b at its inner periphery, which are partially cutand shifted axially toward the transmission, as shown in FIGS. 3 and 4.A disk-shaped body of the second plate 31 is slightly spaced from thesurface on the axially engine side of the flywheel 21 having thefriction surface, however the fixed portions 31 b are in contact withthe surface on the axially engine side of the flywheel 21 having thefriction surface. The bolt 35 projecting axially toward the transmissionis welded to each fixed portion 31 b. The flywheel 21 with the frictionsurface is provided with concavities 21 c and apertures 21 d atpositions corresponding to the fixed portions 31 b and the bolts 35. Theconcavities 21 c are formed at the surface on the axially transmissionside of the flywheel 21 with the friction surface, and the apertures 21d coaxially extend through bottom walls of the concavities 21 crespectively. The foregoing bolt 35 is axially inserted into theaperture 21 d from the axially engine side. The nut 36 is axiallylocated on the transmission side against the concavity 21 c and aperture21 d, and is engaged with the bolt 35. An end surface of the nut 36 isseated on the bottom surface of the concavity 21 c.

[0168] (1-4-2) Low-Rigidity Damper

[0169] The low-rigidity damper 37 is primarily formed of the small coilsprings 45. The small coil spring 45 is much smaller in free length,wire diameter, and coil diameter than the coil spring 33, and has anextremely small rigidity. As shown in FIG. 3, the small coil springs 45are arranged in two of the four window apertures 32 a, and particularlyin the diametrally opposed two window apertures 32 a (i.e., upper andlower window apertures 32 a in FIG. 3). In each window aperture 32 a,the small coil springs 45 are arranged on the opposite sides, in therotational direction, of the coil spring 33. Edges of the windowapertures 32 a and windows 30 a and 31 a support an outer end of eachsmall coil spring 45 in the rotational direction. Therefore, the smallcoil spring 45 operates in series with respect to the coil spring 33. Ineach of the diametrally opposed two windows apertures 32 a, which arelocated on the right and left sides in FIG. 3, among the four windowapertures 32 a, a space 79 of a predetermined angle is maintained in therotational direction between each end of the coil spring 33 and theneighboring end of the window aperture 32 a.

[0170] Description will now be given in greater detail. As shown inFIGS. 8 and 9, a first spring seat 70 is disposed between each smallcoil spring 45 and the corresponding coil spring 33. As shown morespecifically in FIGS. 14 to 17, the first spring seat 70 is formed of asupport portion 81 having a disk-shaped form, a first projection 82, anda second projection 83. The support portion 81 has an annular firstsupport surface 81 a, which comes into contact with the end surface of alarge spring 33 a of the coil spring 33 in the rotational direction. Thefirst projection 82 projects from the first support surface 81 a, andhas an annular second support surface 82 a, which contacts with therotational end surface of a small spring 33 b of the coil spring 33 anda first outer peripheral surface 82 b, which contacts with an innerperipheral surface of the large spring 33 a. The second projection 83projects from the second support surface 82 a of the first projection 82and has a flat end surface 83 a and a second outer peripheral surface 83b which contacts with the inner peripheral surface of the small spring33 b. The support portion 81 also has a second support surface 81 b onthe side opposite to the first support surface 81 a. The second supportsurface 81 b is spaced in the rotational direction from the end surface91 of the window aperture 32 a in the input disk-shaped plate 32 asshown in FIG. 8, however it is in contact with or close to the endsurfaces 94 of the windows 30 a and 31 a in the first and second plates30 and 31.

[0171] As seen in FIG. 17, the first spring seat 70 further has aconcavity 85, which is formed at its end surface remote from the firstand second projections 82 and 83 for inserting the small coil spring 45therein. As shown in FIGS. 16 and 17, the concavity 85 is primarilyformed of first and second portions 86 and 87. The first portion 86 ofthe concavity 85 has a circular caved form when viewed in the rotationaldirection and is formed in a portion corresponding to the secondprojection 83. The second portion 87 of the concavity 85 forms anexternal opening portion extending to the first portion 86, and hassurfaces 88 and 89 which extend from the first portion 86 and divergetoward the external opening. Straight surfaces 88 a and 89 a are ensuredbetween the opening and the respective surfaces 88 and 89. An end of thesmall coil spring 45 is disposed within the concavity 85 of the firstspring seat 70 as shown in FIG. 22 and an end portion thereof isinserted into the first portion 86 of the concavity 85. The end of thefirst spring seat 70 is in contact with the bottom surface of the firstportion 86 of the concavity 85 allow torque transmission. The outerperipheral surface of the end portion of the first spring seat 70 isfitted into the first portion of the concavity 85, and is in contactwith or close to the peripheral surface thereof. In the state describedabove, a small radial space is maintained between the small coil spring45 and the radial surface 88 on the radially inner side, and a largeradial space is maintained between the small coil spring 45 and theradial surface 89 an the radially outer side as shown in FIG. 22.

[0172] As shown in FIGS. 10 to 13, a second spring seat 71 is formed ofa body 72 and a pair of engagement projections 73 and 74. The body 72substantially has a columnar form extending in the axial direction. Asshown in FIGS. 12 and 13, the body 72 has a first concavity 77 on a sidesurface of the small coil spring 45, and also has a second concavity 74on the opposite surface. The second concavity 74 further has a recessedform opened in the tangentially opposite directions. The secondconcavity 74 has a first surface 74 a directed in the rotationaldirection as well as second and third surfaces 74 b and 74 c directed inthe axial direction. In other words, a pair of upper and lower radialprojections 75 and 76 form the second concavity 74. As shown in FIG. 18,the window aperture 32 a in the input disk-shaped plate 32 is furtherprovided with a hollow 97, which is formed at each end surface 91 (i.e.,surface directed substantially in the rotational direction) of thewindow aperture 32 a and is hollowed substantially in the rotationaldirection. The hollow 97 has a first linear surface 97 a directed in therotational direction as well as second surfaces 97 b located on theopposite sides of the first surface 97 a. As shown in FIG. 18, thesecond spring seat 71 is removable in the rotational direction from theend surface 91, but is radially and axially unmovable when it is in theengaged state. More specifically, the first surface 97 a of the hollow97 is in contact with the first surface 74 a of the second concavity 74of the second spring seat 71 so that a torque can be transmitted fromthe second spring seat 71 to the end surface 91. Additionally, a portionnear the first surface 97 a is located axially between the projections75 and 76 so that the second spring seat 71 cannot axially be spacedfrom the input disk-shaped plate 32. Further, the outer peripheralsurface of the body 72 of the second spring seat 71 is in contact withthe second surface 97 b. Therefore, the second spring seat 71 cannot bespaced radially from the input disk-shaped plate 22.

[0173] As shown in FIGS. 10 and 15, the first concavity 77 is a circularform when viewed in the radial direction and has a bottom surface 77 aand a peripheral surface 77 b. As shown in FIG. 18, an end of the smallcoil spring 45 is fitted into the first concavity 77. An end surface,which is substantially directed in the rotational direction, of one endof the small coil spring 45 is in contact with the bottom surface 77 aof the first concavity 77 to enable a transmission of torque. An outerperipheral surface of the end of the small coil spring 45 is in contactwith or close to the peripheral surface 77 b of the first concavity 77,and thus is engaged therewith so that disengagement thereof from thesecond spring seat 71 is prevented.

[0174] As shown in FIG. 19, the end surfaces 94, which are directed inthe rotational direction, of the windows 30 a and 31 a in the first andsecond plates 30 and 31 are further provided with hollows 98, which arefollowed in the rotational direction. The hollow 98 has a semicircularform. As shown in FIG. 19, the second spring seat 71 is removable fromthe end surface 94 in the rotational direction, but is radially andaxially unmovable in the engaged state. More specifically, the surfaces73 a of first and second projections 73 are engaged with the hollow 98in the rotational direction. Therefore, the second spring seat 71 cantransmit a torque to the end surface 94, and the second spring seat 71is not radially spaced from the first and second plates 30 and 31.Further, portions near the hollow 98 are located close to the surfaces72 a on the axially opposite sides of the body 72 respectively so thatthe second spring seat 71 is not axially spaced from first and secondplates 30 and 31.

[0175] As shown in FIG. 3, in the structure already described, since thelow-rigidity damper 37 is located between the coil springs 33neighboring to each other in the rotational direction, it is possible toprevent an unnecessary increase in diameter of the damper mechanism 6.In particular, the small coil spring 45 is located within an annularregion defined between the outermost and innermost peripheries of thecoil spring 33 when viewed in the axial direction. Therefore, diameterof the damper mechanism does not increase beyond necessary length.

[0176] Further, the small coil springs 45 are disposed close to theopposite ends, of the coil spring 33 in the rotational direction andmore specifically are arranged within the window aperture 32 a andothers so that the sizes and required space of the whole dampermechanism 6 can be reduced.

[0177] (1-4-3) Frictional Resistance Generating Mechanism

[0178] as seen in FIGS. 1 and 2, the frictional resistance generatingmechanism 7 functions between the crankshaft 2 and the flywheel 21 withthe friction surface in parallel with the coil springs 33 in therotational direction and generates a predetermined frictional resistance(hysteresis torque) when the crankshaft 2 rotates relatively to theflywheel 21 with the friction surface. As shown in FIG. 5, thefrictional resistance generating mechanism 7 is formed of a plurality ofwashers, which are disposed between the second friction surface 21 b ofthe flywheel 21 having the friction surface and the contact portion 27of the disk-shaped plate 22 and are in contact with each other. As shownin FIGS. 5 and 6, the frictional resistance generating mechanism 7 has acone spring 43 located near the contact portion 27, an output frictionplate 44, an input friction plate 63, and a friction washer unit 61located at positions successively shifted toward the flywheel 21respectively. As described above, the disk-shaped plate 22 has thefunction of holding the frictional resistance generating mechanism 7 onthe side of the flywheel 21 with the friction surface. Therefore, it ispossible to reduce the number of parts and thus the structure can besimplified.

[0179] The cone spring 43 is provided apply a load to each frictionsurface in the axial direction and is compressed between the contactportion 27 and the output friction plate 44 so that it applies an axialconstant biasing force to these members. The output friction plate 44 isprovided with claws 44 a at its outer periphery, which are engaged withthe recesses 26 a in the disk-shaped plate 22, so that the outputfriction plate 44 is unrotatable relatively but is axially movable withrespect to the disk-shaped plate 22 and the flywheel 21 having thefriction surface. The output friction plate 44 has an inner peripheralsurface, which is in contact with the outer peripheral surface 28 a ofthe base portion of the cylindrical portion 28 formed at the innerperiphery of the disk-shaped plate 22, and thereby is radiallypositioned.

[0180] The friction washers 61 are formed of a plurality of arc-shapedmembers aligned in the rotational direction as shown in FIG. 7. As seenin FIG. 6, each friction washer 61 is held between the output frictionplate 44 and the second friction surface 21 b of the flywheel 21 havingthe friction surface. Thus, a radial surface 61 a on the engine side ofthe friction washer 61 is in slidable contact with the output frictionplate 44 and a radial surface 61 b on the transmission side of thefriction washer 61 is in slidable contact with the second frictionsurface 21 b of the flywheel 21 having the friction surface. As shown inFIG. 24, the friction washer 61 is provided with a concavity 62 at itsouter peripheral surface 61 c. The concavity 62 is formed at acircumferentially middle portion of the friction washer 61 and has abottom surface 62 a extending in the rotational direction (i.e.,circumferential direction) as well as inclined surfaces 62 b, whichextend obliquely and radially outward from the opposite ends of thebottom surface 62 a. The inclined portions 62 b on the opposite ends ofeach concavity 62 diverge radially outward to increase thecircumferential distance between them. An inner peripheral surface 61 dof the friction washer 61 has a circumferentially middle portion, whichis close to the outer peripheral surface 28 b of the free end portion ofthe radially inner cylindrical portion 28 and a space between the innerperipheral surface 61 d and the outer peripheral surface 28 b graduallyincreases as the position moves to the circumferential end of the innerperipheral surface 61 d. Thus, the friction washer 61 is swingablearound its circumferentially middle portion with respect to thecylindrical portion 28.

[0181] As shown in FIG. 7, the input friction plate 63 has a disk-shapedportion 63 a disposed radially outside the friction washer 61. As seenin FIG. 5, the input friction plate 63 is provided with a plurality ofprojections 63 b at its outer periphery.

[0182] Referring to FIGS. 5 and 6, the projections 63 b are formedcorresponding to the recesses 26 a respectively and each have aprojected portion 63 c extending radially outward and a claw 63 dextending axially toward the engine from the end of the projectedportion 63 c. The projected portion 63 c extends radially through therecess 26 a. The claw 63 d is located radially outside the cylindricalportion 26, and extends through the recess 20 a in the cylindricalportion 20 of the disk-shaped member 13 from the axially transmissionside. The claw 63 d has a circumferential width (i.e., width in therotational direction) equal to that of the recess 20 a, therefore iscircumferentially unmovable in the recess 20 a.

[0183] As seen in FIG. 7, the disk-shaped portion 63 a of the inputfriction plate 63 has an inner peripheral surface 64 which is opposed tothe outer peripheral surface 61 c of the friction washer 61 with aslight space therebetween, and a plurality of convexities 65 extendingradially inward from the inner peripheral surface 64 into theconcavities 62, respectively. The convexities 65 and the concavities 62form an engagement portion 78 in the frictional resistance generatingmechanism 7. The engagement portion 78 will now be described in greaterdetail. As shown in FIG. 24, the convexity 65 has a substantially squareform and has round corners 65 a. The convexity 65 is close to the bottomsurface 62 a of the concavity 62, and the space 79 of a predeterminedangle, e.g., of 4 degrees is preferably maintained in the rotationaldirection between each corner 65 a and the neighboring inclined surface62 b. A total of these torsion angles on the opposite sides is equal toan allowed maximum angle of relative rotation between the frictionwasher 61 and the input friction plate 63. In this embodiment, the abovetotal torsion angle is equal to 8 degrees (see FIG. 21) and ispreferably equal to or slightly larger than a damper operation anglewhich occurs from depends on minute torsional vibrations caused byvariations in combustion of the engine.

[0184] As described above, friction washer 61 is frictionally engagedwith the members on the output side, i.e., the flywheel 21 with thefriction surface and the output friction plate 44, and is also engagedwith the member on the input side, i.e., the input friction plate 63 viathe rotating-direction space 79 of the engagement portion 78 forallowing torque transmission.

[0185] In the above structure, since the second friction surface 21 b ofthe flywheel 21 with the friction surface forms the friction surface ofthe frictional resistance generating mechanism 7, the number of parts isreduced and the structure becomes simpler.

[0186] Clutch Cover Assembly

[0187] Referring again to FIGS. 1 and 2, the clutch cover assembly 8 isa mechanism bias a friction facing 54 of the clutch disk assembly 9 tothe first frictional surface 21 a of the flywheel 21 having the frictionsurface by an elastic force. The clutch cover assembly 8 is primarilyformed of a clutch cover 48, a pressure plate 49, and a diaphragm spring50.

[0188] The clutch cover 48 is a disk-shaped member prepared by pressworking and has a radially outer portion fixed to the radially outerportion of the flywheel 21 with the friction surface by bolts 51.

[0189] The pressure plate 49, which is made of, e.g., cast iron, isdisposed radially inside the clutch cover 48, and is axially located onthe transmission side with respect to the flywheel 21 having thefriction surface. The pressure plate 49 has a pressing surface 49 aopposed to the first friction surface 21 a of the flywheel 21 having thefriction surface. The pressure plate 49 is provided with a plurality ofarc-shaped projected portions 49 b projecting toward the transmission atthe surface opposite to the pressing surface 49 a. The pressure plate 49is coupled unrotatably and axially movably to the clutch cover 48 by aplurality of arc-shaped strap plates 53. In the clutch engaged state,the strap plates 53 apply a load to the pressure plate 49 for biasingthe pressure plate 49 away from the flywheel 21 with having frictionsurface.

[0190] The diaphragm spring 50 is a disk-shaped member disposed betweenthe pressure plate 49 and the clutch cover 48, and is formed of anannular elastic portion 50 a and a plurality of lever portions 50 bextending radially inward from the elastic portion 50 a. The radiallyouter portion of the elastic portion 50 a is in axial contact with theend of each projected portion 49 b of the pressure plate 49 on thetransmission side.

[0191] The clutch cover 48 is provided with a plurality of tabs 48 a atits inner periphery, which extend axially toward the engine and are bentradially outward. Each tab 48 a extends through an aperture in thediaphragm spring 50 toward the pressure plate 49. The tabs 48 a supporttwo wire rings 52, which support axially opposite sides of the radiallyinner portion of the elastic portion 50 a of the diaphragm spring 50. Inthis state, the elastic portion 50 a is axially compressed to apply anaxial force to the pressure plate 49 and the clutch cover 48.

[0192] Clutch Disk Assembly

[0193] The clutch disk assembly 9 has the friction facing 54 disposedbetween the first friction surface 21 a of the flywheel 21 having thefriction surface and the pressing surface 49 a of the pressure plate 49.The friction facing 54 is fixed to a hub 56 via a circular and annularplate 55. The hub 56 has a central aperture spline-engaged with thetransmission input shaft 3.

[0194] Release Device

[0195] The release device 10 is a mechanism provided to drive thediaphragm spring 50 of the clutch cover assembly 8 to perform the clutchreleasing operation on the clutch disk assembly 9. The release device 10is primarily formed of a release bearing 58 and a hydraulic cylinderdevice (not shown). The release bearing 58 is primarily formed of innerand outer races as well as a plurality of rolling elements arrangedtherebetween and can bear radial and thrust loads. A cylindricalretainer 59 is attached to the outer race of the release bearing 58. Theretainer 59 has a cylindrical portion a first flange, and a secondflange. The cylindrical portion contacts the outer peripheral surface ofthe outer race. The first flange extends radially inward from an axialend on the engine side of the cylindrical portion and is in contact withthe surface on the transmission side of the outer race in the axialdirection. The second flange extends radially outward from an end on theengine side of the cylindrical portion in the axial direction. Thesecond flange is provided with an annular support portion, which is inaxial contact with a portion on the engine side of the radially innerend of each lever portion 50 b of the diaphragm spring 50.

[0196] A hydraulic cylinder device is primarily formed of a hydraulicchamber forming member and a piston 60. The hydraulic chamber formingmember and the cylindrical piston 60 arranged radially inside the memberdefine a hydraulic chamber between them. The hydraulic chamber can besupplied with a hydraulic pressure from a hydraulic circuit. The piston60 has a substantially cylindrical form and has a flange which is inaxial contact with a portion on the transmission side of the inner raceof the release bearing 58. When the hydraulic circuit supplies ahydraulic fluid into the hydraulic chamber, the piston 60 axially movesthe release bearing 58 toward the engine.

[0197] Coupling Between First and Second Flywheel Assemblies

[0198] As already described, each of the first and second flywheelassemblies 4 and 5 is independent of each other and is axially andremovably attached. More specifically, the first and second flywheelassemblies 4 and 5 are engaged together owing to engagement between thecylindrical portion 20 and the input friction plate 63, between thedisk-shaped member 13 and the contact portion 27 (relative rotationsuppressing mechanism 24), between the second plate 31 and the flywheel21 with the friction surface (coupling structure 34), and between thesupport plate 39 and the flywheel 21 with the friction surface (bushing47), which are located at positions shifted successively and radiallyinward in this order. These assemblies 4 and 5 are axially movablethrough a predetermined range with respect to each other. Morespecifically, the second flywheel assembly 5 is axially movable withrespect to the first flywheel assembly 4 between a position, where thecontact portion 27 is slightly spaced from the friction member 19, and aposition, where the contact portion 27 is in contact with the frictionmember 19.

[0199] (2) Operation

[0200] (2-1) Torque Transmission

[0201] In this clutch device 1, a torque is supplied from the engine tothe crankshaft 2 to the flywheel damper 11, and is transmitted from thefirst flywheel assembly 4 to the second flywheel assembly 5 via thedamper mechanism 6. In the damper mechanism 6, the torque is transmittedthrough the input disk-shaped plate 32, small coil springs 45, coilsprings 33, and output disk-shaped plates 30 and 31 in this order.Further, the torque is transmitted from the flywheel damper 11 to theclutch disk assembly 9 in the clutch engaged state and is finallyprovided to the input shaft 3.

[0202] (2-2) Absorbing and Damping of Torsional Vibrations

[0203] When the clutch device 1 receives the combustion variations fromthe engine, the damper mechanism 6 operates to rotate the inputdisk-shaped plate 32 relatively to the output disk-shaped plates 30 and31 in the damper mechanism 6 so that the small coil springs 45 and thecoil springs 33 are compressed. Further, the frictional resistancegenerating mechanism 7 generates a predetermined hysteresis torque.Through the foregoing operations, the torsional vibrations are absorbedand damped.

[0204] As seen in FIGS. 8 and 9, more specifically, the small coilsprings 45 and the coil spring 33 are compressed between the endsurfaces 91 of the window aperture 32 a in the input disk-shaped plate32 and the end surfaces 94 of the windows 30 a and 31 a in the outputdisk-shaped plates 30 and 31 in the rotational direction. Further, in aregion of a small torsion angle, the two small coil springs 45 arecompressed to exhibit characteristics of a low rigidity. In this state,the coil spring 33 is hardly compressed. Moreover, when the inputdisk-shaped plate 32 rotates in the rotational direction R1 relativelyagainst the first and second plates 30 and 31 from the neutral positionillustrated in FIG. 22, the small coil spring 45 located on the forwardside in the rotational direction R2 with respect to the coil spring 33is compressed in the rotational direction between the first and secondspring seats 70 and 71. In this operation, the torque is transmittedfrom the end surface 91, located on the forward side in the rotationaldirection R2, of the window aperture 32 a in the input disk-shaped plate32 to the coil spring 33 via the second spring seat 71 on the forwardside in the rotational direction R2, the small coil spring 45 and thefirst spring seat 70, and further is transmitted through the firstspring seat 70 on the forward side in the rotational direction R1 to theend surfaces 94 on the forward side in the rotational direction R2 ofthe windows 30 a and 31 a in the plates 30 and 31. Thereafter, as shownin FIG. 23, the end surface 91 on the forward side in the rotationaldirection of the window aperture 32 a comes into contact with the secondsupport surface 81 b of the support portion 81 of the first spring seat70. At the same time, a portion of the body 72 of the second spring seat71 comes into contact with the radial surface 89 on the radially outerside of the concavity 85 of the first spring seat 70. When this contactoccurs, the small coil springs 45 are no longer compressed. As describedabove, since the small coil springs 45 are disposed within the windowaperture 32 a in the input disk-shaped plate 32 and are aligned in therotational direction with respect to the coil spring 33, the requiredspaced can be small and the structure can be relatively simple. Further,the radial surface 89 on the radially outer side of the first springseat 70 (i.e., the surface located radially outside the small coilspring) is inclined to increase the space from the small coil spring 45as the position moves toward the end surface 91. Therefore, the firstspring seat 70 does not restrict the radial position of the small coilspring 45 when the small coil spring 45 is compressed. Consequently thesmall coil spring 45 does not slide on the first spring seat 70 so thatfriction hardly occurs therebetween. Further, the small coil spring 45maintains an intended position when compressed, and thus can provide anintended load.

[0205] Subsequently, the coil spring 33 is compressed to producecharacteristics of a high rigidity in a region of a large torsion angle.More specifically, the four coil springs 33 are compressed in parallel.

[0206] Referring now to FIG. 5, in the frictional resistance generatingmechanism 7, the friction washer 61 rotates together with the inputfriction plate 63, and thus rotates relatively to the output frictionplate 44 and the flywheel 21 having the friction surface. Consequently,the friction washer 61 slides on the output friction washer 44 and theflywheel 21 having the friction surface to generate a relatively largefrictional resistance.

[0207] (2-2-1) Minute Torsional Vibrations

[0208] The operation of the damper mechanism 6, which is performed whenminute torsional vibrations due to the combustion variations of theengine are applied to the clutch device 1, will now be described withreference to a mechanical circuit diagram of FIG. 20 as well as torsioncharacteristic diagrams of FIG. 21, 27, 28 and 29. In FIG. 20, the firstand second spring seats 70 and 71 are not shown.

[0209] When minute torsional vibrations are applied, the input frictionplate 63 in the frictional resistance generating mechanism 7 rotatesrelatively to the friction washer 61 through an angle, which correspondsto the minute space in the rotational direction between the concavity 65and convexity 62. Thus, the friction washer 61 is not driven by theinput friction plate 63, and therefore, does not rotate relatively theflywheel 21 having the friction surface and others. Consequently, a highhysteresis torque does not occur in response to the minute torsionalvibrations. According to the torsion characteristic diagram of FIG. 21the coil spring 33 operates, e.g., in “AC2 HYS”, but no sliding occursin the frictional resistance generating mechanism 7. Thus, only ahysteresis torque, which is much smaller than an ordinary hysteresistorque, can be obtained in a predetermined torsion angle range. Asdescribed above, the minute rotating-direction space is provided toprevent the operation of the frictional resistance generating mechanism7 in the predetermined angle range in the torsion characteristics.Therefore, the levels of vibrations and noises can be significantlylowered.

[0210] The operation of driving the friction washer 61 by the inputfriction plate 63 will now be described in connection with an initialtransition state and a usual state. The input friction plate 63 rotatesrelatively to the friction washer 61 in the rotational direction R1 fromthe neutral position in FIG. 24, as described below. In FIG. 24, theinner peripheral surface 61 d of the friction washer 61 is slightlyspaced from the outer peripheral surface 28 b of the cylindrical portion28 except for its circumferentially middle portion (i.e., the middleportion in the rotational direction).

[0211] When the torsion angle increases, the convexity 65 comes intocontact with the wall surface of the convexity 62 as shown FIG. 25. Morespecifically, the corner 65 a of the convexity 65 comes into contactwith the inclined surface 62 b of the convexity 62. In this state, acomponent of a force applied from the convexity 65 to the concavity 62occurs to move the friction washer 61 radially inward. When the torsionangle increases from the state shown in FIG. 25, the portion, which islocated on the forward side in the rotational direction R1, of thefriction washer 61 moves radially inward and the portion on the forwardside in the rotational direction R2 moves radially outward. Thus, asshown in FIG. 26, the inner peripheral surface 61 d of the forwardportion of the friction washer 61 in the rotational direction R1 movestoward the outer peripheral surface 28 b of the cylindrical portion 28and the inner peripheral surface 61 d of the forward portion, in therotational direction R2, moves away from the outer peripheral surface 28b of the cylindrical portion 28. During the above operation, the forcefor moving the friction washer 61 radially inwardly increases. Thus, aneffective radius of the friction surface of the friction washer 61gradually increases; thereby the frictional resistance graduallyincreases. After the inner peripheral surface 61 d of the forwardportion of the friction washer 61 the rotational direction R1 comes intocontact with the outer peripheral surface 28 b of the cylindricalportion 28 as shown in FIG. 26, the friction washer 61 moves only in therotational direction thereafter.

[0212] The above can be summarized as follows. The friction washer 61 isdriven by the input friction plate 63 in the two regions, i.e., thefirst region, in which the effective radius of the friction surface andthe frictional resistance gradually increase and the second region, inwhich the effective radius of the friction surface and the frictionalresistance are constant. In this embodiment, the first region has asize, e.g., of about 2°.

[0213] In summary, the input friction plate 63 and the engagementportion 78 of the friction washer 61 (specifically, the convexity 65 andthe concavity 62) are configured to ensure the first region forgradually increasing the effective radius of the friction surface of thefriction washer 61 and the second region for keeping the effectiveradius of the friction surface of the friction washer 61 at a constantvalue.

[0214] Consequently, when the operation angle of the torsionalvibrations does not exceed a predetermined angle (e.g., of 80) of theengagement portion 78, a large frictional resistance (high hysteresistorque) does not occur, and only a region A of a low frictionalresistance is obtained as illustrated in FIG. 27. When the operationangle of the torsional vibrations is in a range between thepredetermined angle (e.g., of 8°) of the rotating-direction space 79 ofthe engagement portion 78 and an angle (e.g., 10°) larger than thispredetermined angle (e.g., 8°) by a frictional resistance change angle(e.g., 2°), a region B in which the frictional resistance graduallyincreases, occurs at each end of the region A of the low frictionalresistance as illustrated in FIG. 28. When the operation angle of thetorsional vibrations is larger than the angle equal to a sum of thepredetermined angle of the engagement portion 78 and the frictionalresistance change angle, the region B, in which the frictionalresistance gradually increases, and a region C, in which a largeconstant frictional resistance occurs, are formed on each side of theregion A of the low frictional resistance as illustrated in FIG. 29.

[0215] (2-2-2) Large-Angle Torsional Vibrations

[0216] Referring now to FIGS. 5, 7 and 21, described before, when thetorsion angle of torsional vibrations is large, the friction washer 61slides on the flywheel 21 having the friction surface and thedisk-shaped plate 22. Thereby, a frictional resistance of a constantmagnitude occurs throughout the first and second stage.

[0217] At an end of the torsion angle range (i.e., the position wherethe direction of the vibration changes), operations are performed asfollows. On the right end in the torsion characteristic diagram of FIG.21, the friction washer 61 is in the position shifted to the maximumextent in the rotational direction R2 with respect to the input frictionplate 63. When the disk-shaped member 13 rotates relatively to theflywheel 21 having the friction surface in the rotational direction R2,the friction washer 61 rotates relatively to the input friction plate 63throughout the angle range of the rotating-direction space 79 betweenthe convexity 65 and the concavity 62. During this operation, thefriction washer 61 does not slide on the member on the output side sothat the region A (e.g., of 8°) of a low frictional resistance isobtained. When the rotating-direction space 79 of the engagement portion78 disappears the input friction plate 63 starts to drive the frictionwasher 61. Thereby, the friction washer 61 rotates relatively to theoutput friction plate 44 and the flywheel 21 having the friction surfaceas well as the disk-shaped plate 22. This produces the region B, e.g.,of 2°, in which the frictional resistance gradually (and thus smoothly)increases, as already described, then produces the region C of a largeconstant frictional resistance.

[0218] As described above, the region B, in which the frictionalresistance gradually increases, is provided in an initial stage of theoperation of generating a large frictional resistance. Since the largefrictional resistance rises smoothly, a wall of a high hysteresis torquedoes not exist when generating the large hysteresis torque. Thereby,hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism, which is provided with the minute space in therotational direction for absorbing the minute torsional vibrations.

[0219] In particular, since the structure according to the inventionemploys a single kind of friction washers (i.e., washers 61) forgenerating an intermediate frictional resistance, the kinds of thefriction members can be reduced in number. Since the friction washer 61has a simple arc-shaped form, the manufacturing cost thereof can be low.

[0220] (3) Clutch Engaging and Releasing Operations

[0221] As seen in FIGS. 1 and 2, when the hydraulic circuit (not shown)supplies the hydraulic fluid into the hydraulic chamber of the hydrauliccylinder, the piston 60 axially moves toward the engine. Thereby, therelease bearing 58 axially moves the radially inner end of the diaphragmspring 50 toward the engine. Consequently, the elastic portion 50 a ofthe diaphragm spring 50 is spaced from the pressure plate 49. Thereby,the pressure plate 49 biased by the strap plates 53 moves away from thefriction facing 54 of the clutch disk assembly 9 so that the clutch isreleased.

[0222] In the clutch release operation, the release bearing 58 appliesan axial load which is directed toward the engine to the clutch coverassembly 8 and this load axially biases and moves the second flywheelassembly 5 toward the engine. Thereby, the contact portion 27 of thedisk-shaped plate 22 in the relative rotation suppressing mechanism 24is pressed against the friction mechanism 19 and is frictionally engagedwith the disk-shaped member 13. Thus, the second flywheel assembly 5becomes unrotatable with respect to the first flywheel assembly 4. Inother words, the second flywheel assembly 5 is locked with respect tothe crankshaft 2 so that the damper mechanism 6 does not operate.Accordingly, when the rotation speed passes through the resonance pointin a low speed range (e.g., from 0 to 500 rpm) during a start or stopoperation of the engine, it is possible to suppress the breakage of thedamper mechanism 6 as well as noises and vibrations, which may be causedby the resonance when releasing the clutch.

[0223] In this operation, since the damper mechanism 6 is locked byusing the load applied from the release device 10 in the clutchreleasing operation, the structure becomes simpler. In particular, sincethe relative rotation suppressing mechanism 24 is formed of the membershaving simple forms such as the disk-shaped member 13 and thedisk-shaped plate 22, a special structure is not required.

[0224] (3) Stop Mechanism of Damper Mechanism

[0225] As already described, the elastic coupling mechanism 29 of thedamper mechanism 6, which elastically couples the second flywheelassembly 5 to the crankshaft 2 in the rotating direction, is formed ofthe pair of output-side disk-shaped plates 30 and 31, the input-sidedisk-shaped plate 32, and a plurality of coil springs 33. As seen inFIG. 3, further, a stop mechanism 90 of the damper mechanism 6 is formedof a plurality of plate coupling portions 40 formed at the outerperiphery of the disk-shaped main body of the second plate 31 and thecontact portions 32 c formed at the outer periphery of the input-sidedisk-like plate 32.

[0226] The stop mechanism 90 described above has the followingadvantages.

[0227] (3-1) Since the axially extending portion 41 of the platecoupling portion 40 has a plate-like form, a circumferential anglethereof can be shorter than that in a conventional stop pin.

[0228] (3-2) The axially extending portion 41 of the plate couplingportion 40 has a radial length much smaller than that of theconventional stop pin. More specifically, the radial length of the stopmechanism 90 is equal to the thickness of the pair of output-sidedisk-shaped plates 30 and 31. This means that the radial length of thestop mechanism 90 is substantially restricted to a small valuecorresponding to the plate thickness.

[0229] Owing to the above, as shown in FIG. 3, the plate couplingportion 40 is arranged at the outer peripheral portion, i.e., theradially outermost position of the input disk-shaped plate 32, and islocated radially outside the outer periphery of the window aperture 32a. As described above, the plate coupling portion 40, i.e., the stopmechanism 90 takes a position radially different from the windowaperture 32 a so that the stop mechanism 90 does not circumferentiallyinterfere with the window aperture 32 a. Consequently, it is possible toincrease both the maximum torsion angle of the damper mechanism 6 andthe torsion angle of the coil spring 33. More specifically, the platecoupling portion 40 moves to a position radially outside the windowaperture 32 a, and further can substantially move to a position radiallyoutside a circumferential center of the window aperture 32 a.

[0230] In a conventional structure, the stop mechanism and the windowaperture are located at the radially same position. In this structure,the torsion angle of the damper mechanism restricts the circumferentialangle of the window aperture, and vice versa so that it is impossible toincrease the maximum angle of the damper mechanism and to lower therigidity of the springs.

[0231] In particular, the radial length of the stop mechanism 90 is muchshorter than that of the conventional stop pin. Therefore, provision ofthe stop mechanism radially outside the window aperture 32 a does notremarkably increase the outer diameter of the output-side disk-shapedplates 30 and 31. Also, it does not reduce the radial length of thewindow aperture 32 a.

Alternate Embodiments

[0232] Alternate embodiments will now be explained. In view of thesimilarity between the first and alternate embodiments, the parts of thealternate embodiments that are identical to the parts of the firstembodiment will be given the same reference numerals as the parts of thefirst embodiment. Moreover, the descriptions of the parts of thealternate embodiments that are identical to the parts of the firstembodiment may be omitted for the sake of brevity.

[0233] Second Embodiment

[0234] Referring to FIGS. 30 to 45, a second embodiment of the inventionwill be described. Basic structures of the clutch device and the dampermechanism in the second embodiment are substantially the same as thosein the first embodiment as a whole, therefore, a frictional resistancegenerating mechanism 107 will be described hereinafter.

[0235] As seen in FIG. 30, the frictional resistance generatingmechanism 107 functions between a crankshaft and a flywheel 121 havingthe friction surface in parallel with coil springs 133 and generates apredetermined frictional resistance (hysteresis torque) when thecrankshaft rotates relatively to the flywheel 121 having the frictionsurface. As seen in FIG. 30 the frictional resistance generatingmechanism 107 is formed of a plurality of washers, which are disposedbetween a second friction surface 121 b of the flywheel 121 having thefriction surface and a contact portion 127 of a disk-shaped plate 122,and are in contact with each other. As shown in FIGS. 30 and 31, thefrictional resistance generating mechanism 107 has a cone spring 143, anoutput friction plate 144, a first friction washer 161, a first frictionwasher 162, an input friction plate 163, a second friction washer 164,and a second friction washer 165. The cone spring 143 is located nearthe contact portion 127. The first friction washer 161 has a highfriction coefficient. The first friction washer 162 has a low frictioncoefficient. The second friction washer 164 has a low frictioncoefficient. The second friction washer 165 has a high frictioncoefficient. In the aforementioned order, the members of the frictionalresistance generating mechanism 107 are located at positionssuccessively shifted toward the flywheel 121, respectively. As describedabove, the disk-shaped plate 122 has the function of holding thefrictional resistance generating mechanism 107 on the side of theflywheel 121 having the friction surface. Therefore, it is possible toreduce the number of parts to simplify the structure.

[0236] The cone spring 143 is provided apply an axial load to eachfriction surface and is compressed between the contact portion 127 andthe output friction plate 144 so that it applies an axial biasing forceto these members. The output friction plate 144 is provided with claws144 a at its outer periphery, which are engaged with recesses 126 a inthe disk-shaped plate 122 so that the output friction plate 144 isunrotatable but is axially movable with respect to the disk-shaped plate122 and the flywheel 121 having the friction surface. The outputfriction plate 144 has an inner peripheral surface, which is in contactwith an outer peripheral surface 128 a of the base portion of thecylindrical portion 128 formed at the outer periphery of the disk-shapedplate 122, and thereby is radially positioned.

[0237] The first friction washer 161 having a high friction coefficientis an annular member as shown in FIGS. 32 and 33. As shown in FIG. 31,the first friction washer 161 is located between the output frictionplate 144 and the first friction washer 162 having a low frictioncoefficient. The first high-friction-coefficient friction washer 161 isformed of a core plate 171 and a friction facing 172 affixed thereto.The core plate 171 is an annular member. The friction facing 172 isformed of a plurality of arc-shaped members affixed to the axial surfaceon the engine side of the core plate 171, and is in contact with theoutput friction plate 144. The core plate 171 and the friction facing172 have substantially the same inner diameters, and also havesubstantially the same outer diameters. As seen in FIGS. 32 and 33, thecore plate 171 is provided with projected portions 171 a at its outerperiphery projecting axially toward the transmission. The core plate 171is provided with a plurality of apertures 171 b at its body. The coreplate 171 is provided with a plurality of projections 171 c at its innerperiphery extending radially inward. The friction facing 172 is providedwith apertures 172 a corresponding to the apertures 171 b respectively.

[0238] As shown in FIG. 34, the first low-friction-coefficient frictionwasher 162 is formed of a plurality of arc-shaped members, and as seenin FIG. 31, is located between the first high-friction-coefficientfriction washer 161 and the input friction plate 163. The firstlow-friction-coefficient friction washer 162 is preferably made ofplastics. Referring again to FIG. 34, the first low-friction-coefficientfriction washer 162 is provided with a plurality of projected portions162 a at its radial surface on the engine side. The projected portions162 a are inserted into and engaged with the apertures 171 b and 172 ain the first high-friction-coefficient friction washer 161. Owing tothis engagement, the first high-friction-coefficient friction washer 161and first low-friction-coefficient friction washer 162 rotate together.The first low-friction-coefficient friction washer 162 is provided witha plurality of projections 162 b at its inner periphery projectedradially inward.

[0239] The input friction plate 163 has a disk-shaped portion 163 alocated axially between the first low-friction-coefficient frictionwasher 162 and the second low-friction-coefficient friction washer 164.As shown in FIG. 35, the input friction plate 163 is provided with aplurality of projections 163 b at its outer periphery, as shown in FIG.35. The projections 163 b are formed corresponding to the recesses 126a, respectively, and each are formed of a projected portion 163 cprojected radially outward and a claw 163 d extending axially toward theengine from the end of the projected portion 163 c. The projectedportion 163 c extends radially through the recess 126 a. The claw 163 dis located radially outside the cylindrical portion 126, and extendsaxially through the recess 126 a in the cylindrical portion 120 of thedisk-shaped member 113 toward the engine. As shown in FIGS. 39 and 40,the claw 163 d and the recess 120 a form a first rotating-directionengagement portion 181 between the disk-shaped member 113 and the outputfriction plate 144. The disk-shaped portion 163 a of the input frictionplate 163 is provided with a plurality of recesses 163 e at its outerperiphery, and is provided with a plurality of projections 163 f at itsinner periphery extending radially inward.

[0240] In the first rotating-direction engagement portion 181, the widthin the rotational direction of the claw 163 d is shorter than that ofthe recess 120 a so that the claw 163 d can move a predetermined anglewithin the recess 120 a. This means that the input friction plate 163 ismovable through a predetermined angle range with respect to thedisk-shaped member 113. More specifically, as shown in FIG. 40, arotating-direction space 146 of a torsion angle of θ1 is ensured on theforward side, in the rotational direction R2, of the claw 163 d, and arotating-direction space 147 of a torsion angle of θ2 is formed on theforward side, in the rotational direction R1, of the claw 163 d.Consequently, the total torsion angle. i.e. the sum of the torsionangles of θ1 and θ2 provides the predetermined angle, by which the inputfriction plate 163 can rotate relatively to the disk-shaped member 113.In this embodiment, the total torsion angle is equal to 8° (see FIG.42). This total torsion angle is preferably in a range slightlyexceeding a damper operation angle, which is caused by minute torsionalvibrations due to combustion variations of the engine.

[0241] As seen in FIG. 31, the second low-friction-coefficient frictionwasher 164 is formed of a plurality of arc-shaped members similar oridentical to the first low-friction-coefficient friction washer 162 andis located between the input friction plate 163 and the secondhigh-friction-coefficient friction washer 165. The secondlow-friction-coefficient friction washer 164 is preferably made ofplastics. The second low-friction-coefficient friction washer 164 isprovided with a plurality of projected portions 164 a at its surface onthe transmission side.

[0242] The second high-friction-coefficient friction washer 165 is anannular member as shown in FIGS. 36 and 37, and is located between thesecond low-friction-coefficient friction washer 164 and the secondfriction surface 121 b of the flywheel 121 having the friction surface.The second high-friction-coefficient friction washer 165 is formed of acore plate 173 and a friction facing 174 affixed thereto. The core plate173 is an annular member. The friction facing 174 is formed of aplurality of arc-shaped members affixed to the surface on the engineside of the core plate 173 and is in contact with the second frictionsurface 121 b of the flywheel 121 having the friction surface. The innerdiameter of the core plate 173 is substantially equal to the innerdiameter of the friction facing 174, and the inner diameter of the coreplate 173 is slightly larger than the inner diameter of the frictionfacing 174. The core plate 173 is provided with a plurality of apertures173 a at its body. The core plate 173 is provided with a plurality ofprojections 173 c at the inner periphery of the body extending radiallyinward. The friction facing 174 is provided with apertures 174 acorresponding to the respective apertures 173 a. The projected portions164 a of the second low-friction-coefficient friction washer 164 areinserted into and engaged with these apertures 171 b and 172 a. Owing tothis engagement, the second high-friction-coefficient friction washer165 and second low-friction-coefficient friction washer 164 rotatetogether.

[0243] The core plate 173 is provided with a plurality ofcircumferentially spaced recesses 173 b at its outer periphery. Theaxially projected portions 171 a already described are inserted into andengaged with the recesses 173 b, respectively, so that the firsthigh-friction-coefficient friction washer 161 and the secondhigh-friction-coefficient friction washer 165 rotate together. Theaxially projected portions 171 a are inserted into the recesses 163 eformed at the outer periphery of the disk-shaped portion 163 a of theinput friction plate 163, respectively. As described above, the axiallyprojected portions 171 a and the recesses 163 e form a secondrotating-direction engagement portion 182 between the input frictionplate 163 and the friction washers 161, 162, 164 and 165, as shown inFIG. 41.

[0244] In the second rotating-direction engagement portion 182, thewidth in the rotational direction of the axially projected portion 171 ais shorter than that of the recess 163 e so that the axially projectedportion 171 a can move a predetermined angle within the recess 163 e.This means that the input friction plate 163 is movable through apredetermined angle range with respect to the friction washers 161, 162,164, and 165. More specifically, as shown in FIG. 40, arotating-direction space 185 of a torsion angle of θ3 is ensured on theforward side, in the rotational direction R1, of the axially projectedportion 171 a, and a rotating-direction space 186 of a torsion angle ofθ4 is formed on the forward side, in the rotational direction R2 of theprojected portion 171 a. Consequently, the total torsion angle, i.e.,the sum of the torsion angles of θ3 and θ4 provides the predeterminedangle, by which the input friction plate 163 can rotate relatively tothe friction washers 161, 162, 164, and 165. In this embodiment, thetotal torsion angle is equal to 2° (see FIG. 42).

[0245] Referring again to FIG. 31, the frictional resistance generatingmechanism 107 further includes a bushing 166. The bushing 166 is formedof a plurality of members for radially supporting the respective washerswith respect to the inner cylindrical portion 128 and is disposedradially between the inner peripheries of the washers and the innercylindrical portion 128. As seen in FIG. 38, the bushing 166 has apredetermined axial length, and each portion thereof has an arc-shapedform when viewed in the axial direction. The bushing 166 has a smoothinner peripheral surface, which is rotatably supported by an outerperipheral surface 128 b of the free end portion of the innercylindrical portion 128. The inner cylindrical portion 128 is providedwith a plurality of concavities 166 a at its outer peripheral surface.Each concavity 166 a is concaved radially inward, and extends throughoutthe axial length of the portion 128. Into the concavities 166 a,projections of various members are fitted, and specifically, theprojections 171 c of the first high-friction-coefficient friction washer161, the projections 162 b of the first low-friction-coefficientfriction washer 162, projections 164 b of the secondlow-friction-coefficient friction washer 164, the projections 173 c ofthe second high-friction-coefficient friction washer 165, and others arefitted and engaged. A relatively large space in the rotational directionis ensured in the engagement portion, where each washer is engaged withthe bushing 166 so that the foregoing function of the secondrotating-direction engagement portion 182 may not be impeded.

[0246] As seen in FIG. 31, in the frictional resistance generatingmechanism 107 described above, the engagement of the disk-shaped portion163 a of the input friction plate 163 with the first and secondlow-friction-coefficient friction washers 162 and 164 provides a firstfrictional resistance generating portion 188. Further, a secondfrictional resistance generating portion 189 is provided by theengagement between the first high-friction-coefficient friction washer161 and the output friction plate 144 as well as the engagement betweenthe second high-friction-coefficient friction washer 165 and theflywheel 121 having the friction surface.

[0247] In the above structure, since the second friction surface 121 bof the flywheel 121 with the friction surface forms the friction surfaceof the frictional resistance generating mechanism 107, this reduces thenumber of parts and simplifies the structure.

[0248] (2) Operation

[0249] When the clutch device receives the combustion variations fromthe engine, the damper mechanism operates to rotate the inputdisk-shaped plate 132 relatively to the output disk-shaped plates 130and 131 in the damper mechanism so that the plurality of coil springs133 and others are compressed between them. Further, the frictionalresistance generating mechanism 107 generates a predetermined hysteresistorque. Through the foregoing operations, the torsional vibrations areabsorbed and damped. More specifically, the coil springs 133 arecompressed between the circumferential ends of the window apertures inthe input disk-shaped plate 132 and the circumferential ends of thewindows in the output disk-shaped plates 130 and 131.

[0250] As seen in FIGS. 30 and 31, in the frictional resistancegenerating mechanism 107, the first and second high-friction-coefficientfriction washers 161 and 165 rotate together with the disk-shaped member113 via the input friction plate 163 therebetween, and rotatesrelatively to the output friction plate 144 and the flywheel 121 havingthe friction surface. Consequently, sliding occurs between the outputfriction plate 144 and the first high-friction-coefficient frictionwasher 161, and also occurs between the second high-friction-coefficientfriction washer 165 and the flywheel 121 having the friction surface.Thus, the second frictional resistance generating mechanism 189 operatesto generate a relatively large frictional resistance.

[0251] Description will now be given on the operation of the dampermechanism, which is performed when minute torsional vibrations due tothe combustion variations of the engine are applied to the clutchdevice, with reference to a mechanical circuit diagram of FIG. 41 and atorsion characteristic diagram of FIG. 42. When minute torsionalvibrations are applied to the damper mechanism, in which the coilsprings 133 are in the compressed state, the input friction plate 163 ofthe frictional resistance generating mechanism 107 rotates in the minuterotating-direction space (146 and 147), which is defined in the recess120 a of the cylindrical portion 120 of the disk-shaped member 113 bythe claw 163 d, and therefore, relatively rotates the disk-shaped member113. Thus, the disk-shaped member 113 does not drive the input frictionplate 163 and the friction washers 161, 162, 164, and 165. Therefore,neither of the first or second frictional resistance generating portions188 and 189 generates a frictional resistance (see FIG. 43).Consequently, a high hysteresis torque does not occur in response to theminute torsional vibrations. For example, in “AC2 HYS” illustrated inthe torsion characteristic diagram of FIG. 42, the coil springs 133operate, but no sliding occurs in the frictional resistance generatingmechanism 107. In the predetermined torsion angle range, only ahysteresis torque, which is much smaller than an ordinary hysteresistorque, can be obtained. As described above, the structure employs theminute rotating-direction space (146 and 147), which does not operatethe frictional resistance generating mechanism 107 within apredetermined angle range in the torsion characteristics. Therefore, thelevels of the vibrations and noises can be significantly reduced.

[0252] When the torsion angle of the minute torsional vibrations exceedsthe angle of the first rotating-direction engagement portion 181, therotating-direction space (146 and 147) disappears in the firstrotating-direction engagement portion 181, and then the disk-shapedmember 113 drives the input friction plate 163 in the rotationaldirection. Consequently, the input friction plate 163 rotates relativelyto the first and second low-friction-coefficient friction washers 162and 164. Thus, the first frictional resistance generating portion 188operates to generate a relatively small frictional resistance (see FIG.44).

[0253] When the torsion angle of the torsional vibrations furtherincreases, the circumferential space (185 and 186) in the secondrotating-direction engagement portion 182 disappears and the inputfriction plate 163 drives the friction washers 161, 162, 164, and 165 inthe rotational direction. Thereby, the friction washers 161, 162, 164and 165 rotate relatively to the output friction plate 144 and theflywheel 121 having the friction surface. Thus, the second frictionalresistance generating portion 189 operates to generate a relativelylarge frictional resistance (see FIG. 45).

[0254] (2-2-2) Large-Angle Torsional Vibrations

[0255] As already described, when the torsion angle of the torsionalvibrations is large, sliding occurs between the output friction plate144 and the first high-friction-coefficient friction washer 161 andsliding also occurs between the second high-friction-coefficientfriction washer 165 and the flywheel 121 having the friction surface.

[0256] At an end of the torsion angle range (i.e., the position wherethe direction of the vibration changes), operations are performed asfollows. On the right end in the torsion characteristic diagram of FIG.42 the input friction plate 163 is in the position shifted in therotational direction R2 to the maximum extent with respect to thedisk-shaped member 113 and the friction washers 161, 162, 164, and 165are in the positions shifted to the maximum extent in the rotationaldirection R2 with respect to the input friction plate 163. When thedisk-shaped member 113 rotates relatively to the flywheel 121 having thefriction surface in the rotational direction R2, the disk-shaped member113 angularly moves throughout the rotating-direction space (146 and147) of the first rotating-direction engagement portion 181 and rotatesrelatively to the input friction plate 163. During this operation,neither of the first and second frictional resistance generatingportions 188 and 189 generate the frictional resistance. When therotating-direction space (146 and 147) in the first rotating-directionengagement portion 181 disappears, the disk-shaped member 113 drives theinput friction plate 163. Thereby, the input friction plate 163angularly moves throughout the rotating-direction space (185 and 186) inthe second rotating-direction engagement portion 182, and rotatesrelatively to the first and second low-friction-coefficient frictionwashers 162 and 164. During this operation, the first frictionalresistance generating portion 188 operates to generate a relativelysmall frictional resistance.

[0257] As the rotating-direction space (185 and 186) in the secondrotating-direction engagement portion 182 disappears, the input frictionplate 163 drives the friction washers 161, 162, 164, and 165. Thereby,the friction washers 161, 162, 164, and 165 rotate relatively to theoutput friction plate 144 and the flywheel 121 having the frictionsurface. Thereby, the second frictional resistance generating portion189 operates to generate a large frictional resistance.

[0258] As described above, the first frictional resistance generatingportion 188 generates a frictional resistance of an intermediatemagnitude within the torsion angle range of the rotating-direction space(185 and 186) in the second rotating-direction engagement portion 182before the second frictional resistance generating portion 189 operatesto generate a large frictional resistance. As described above, the largefrictional resistance rises in a multi-step or stepwise fashion so thata wall of a high hysteresis torque does not exist when generating thelarge frictional resistance. Thereby, hitting or tapping noises ofclaws, which may occur when a high hysteresis torque occurs, can bereduced in the frictional resistance generating mechanism which isprovided with the minute space in the rotational direction for absorbingthe minute torsional vibrations.

[0259] In the prior art, because the frictional resistance generatingmechanism 107 does not have the second rotating-direction engagementportion 182 and the first frictional resistance generating portion 188,the second frictional resistance generating portion 189 starts theoperation when the claw 163 d in the first rotating-direction engagementportion 181 comes into contact with the recess 120 a in the disk-shapedmember 113. Thereby, a high hysteresis torque rapidly occurs so that theclaws hit the wall to generate the hitting noises.

[0260] Third Embodiment

[0261] (3-1) Structure of Frictional Resistance Generating Mechanism

[0262] Referring initially to FIG. 46, description will now be given ona frictional resistance generating mechanism 207 according to a thirdembodiment of the invention. This frictional resistance generatingmechanism 207 differs from the frictional resistance generatingmechanism 107 of the second embodiment in that the firstrotating-direction engagement portion in the second embodiment isarranged outside the washers and others which are axially stackedtogether, but the first rotating-direction engagement portion in thisembodiment is arranged within axially stacked washers and others.

[0263] The following description will be primarily given on thefrictional resistance generating mechanism 207, and other portions ofthe clutch device will be omitted. Parts and portions corresponding tothose in the preceding embodiments are indicated by reference numbersbearing “2” at the hundred's place.

[0264] The frictional resistance generating mechanism 207 is configuredto operate in the rotational direction between a crankshaft and aflywheel 221 having a friction surface, and in parallel with coilsprings 233 and to generate a predetermined frictional resistance(hysteresis torque) when relative rotation occurs between the crankshaftand the flywheel 221 having a friction surface. The frictionalresistance generating mechanism 207 is formed of a plurality of washers,which are in contact with each other and are disposed between a secondfriction surface 221 b of the flywheel 221 having the friction surfaceand a contact portion 227 of the disk-shaped plate 222. As shown inFIGS. 46 and 47, the frictional resistance generating mechanism 207 hasa cone spring 243 located near the contact portion 227, an outputfriction plate 244, a first friction washer 261 having a high frictioncoefficient, a first friction washer 262 having a low frictioncoefficient, an input friction plate 263, a second friction washer 264having a low friction coefficient, and a second friction washer 265having a high friction coefficient. In this order, these members arelocated at positions successively shifted toward the flywheel 221respectively.

[0265] The cone spring 243 is provided to apply an axial load to eachfriction surface and is compressed between the contact portion 227 andthe output friction plate 244 so that it applies an axial biasing forceto these members. The output friction plate 244 is provided with claws244 a at its outer periphery, which are engaged with the recesses 226 ain the disk-shaped plate 222, so that the output friction plate 244 isunrotatable but is axially movable with respect to the disk-shaped plate222 and the flywheel 221 having the friction surface. The outputfriction plate 244 has an outer peripheral surface, which is in contactwith an inner peripheral surface 228 a of the base portion of acylindrical portion 228 formed at the outer periphery of the disk-shapedplate 222, and thereby is radially positioned.

[0266] The first friction washer 261 having a high friction coefficientis an annular member, and is located between the output friction plate244 and the first friction washer 262 having a low friction coefficient.The first high-friction-coefficient friction washer 261 is formed of acore plate 271 and a friction facing 272 affixed thereto. The core plate271 is an annular member. The friction facing 272 is formed of aplurality of arc-shaped members affixed to the radial surface on theengine side of the core plate 271, and is in contact with the outputfriction plate 244. The core plate 271 is provided with a plurality ofapertures 271 a extending in the rotational direction.

[0267] The first low-friction-coefficient friction washer 262 is formedof a plurality of arc-shaped members, and is located between the firsthigh-friction-coefficient friction washer 261 and the input frictionplate 263. The first low-friction-coefficient friction washer 262 ispreferably made of plastics. The first low-friction-coefficient frictionwasher 262 has apertures 262 a corresponding to the apertures 271 a.Each aperture 271 a is longer in the rotational direction than theaperture 262 a, and has the opposite ends located circumferentially(i.e., in the rotational direction) outside the aperture 262 a.

[0268] The input friction plate 263 has a disk-shaped portion 263 alocated axially between the first low-friction-coefficient frictionwasher 262 and the second low-friction-coefficient friction washer 264.The input friction plate 263 is provided with a plurality of projections263 b at its outer periphery as shown in the figure. The projections 263b are formed corresponding to the recesses 226 a respectively and eachare formed of a projected portion 263 c projected radially outward and aclaw 263 d extending axially toward the engine from the end of theprojected portion 263 c. The projected portion 263 c extends radiallythrough the recess 226 a. The claw 263 d is located radially outside thecylindrical portion 226 and extends axially through a recess 220 a inthe cylindrical portion 220 of the disk-shaped member 213 toward theengine. In contrast to the foregoing embodiment, the claw 263 d is incontact with the edge of the recess 220 a without a space in therotational direction.

[0269] The input friction plate 263 is provided with apertures 263 e atthe disk-shaped portion 263 a corresponding to the apertures 262 arespectively.

[0270] The second low-friction-coefficient friction washer 264 is formedof a plurality of arc-shaped members similar to the firstlow-friction-coefficient friction washer 262, and is located between theinput friction plate 263 and the second high-friction-coefficientfriction washer 265. The second low-friction-coefficient friction washer264 is preferably made of plastics. The second low-friction-coefficientfriction washer 264 is provided with a plurality of first projectedportions 264 a at its surface on the transmission side. Each firstprojected portion 264 a is circumferentially long, and has roundedopposite ends. The first projected portion 264 a is inserted into theaperture 263 e in the disk-shaped portion 263 a, and the end thereof isin contact with the first low-friction-coefficient friction washer 262.The second low-friction-coefficient friction washer 264 has secondprojected portions 264 b, which extend axially toward the transmissionfrom the first projected portions 264 a, respectively. Each secondprojected portion 264 b is circumferentially long and has roundedopposite ends. The second projected portion 264 b is smaller in theradial and circumferential directions than the first projected portion264 a. The second projected portions 264 b are inserted into theapertures 262 a in the first low-friction-coefficient friction washer262 respectively and are engaged therewith in the rotational direction.Owing to this engagement, the first low-friction-coefficient frictionwasher 262 rotates together with the second low-friction-coefficientfriction washer 264. Further, the second projected portions 264 b areinserted into the apertures 271 a in the first high-friction-coefficientfriction washer 261, respectively.

[0271] The second high-friction-coefficient friction washer 265 is anannular member, and is located between the secondlow-friction-coefficient friction washer 264 and the second frictionsurface 221 b of the flywheel 221 having the friction surface. Thesecond high-friction-coefficient friction washer 265 is formed of a coreplate 273 and a friction facing 274 affixed thereto. The core plate 273is an annular member. The friction facing 274 is formed of a pluralityof arc-shaped members affixed to the surface on the engine side of thecore plate 273, and is in contact with the second friction surface 221 bof the flywheel 221 having the friction surface. The core plate 273 isprovided with projected portions 273 a at its body extending axiallytoward the transmission. The projected portions 273 a are inserted intoconcavities 264 c in the second low-friction-coefficient friction washer264.

[0272] As shown in FIG. 48, the first projected portions 264 a of thesecond low-friction-coefficient friction washer 264 and the apertures263 e in the input friction plate 263 form a first rotating-directionengagement portion 281. In the first rotating-direction engagementportion 281, the circumferential width of the first projected portion264 a is shorter than that of the aperture 263 e. Therefore, the firstprojected portion 264 a can move through a predetermined angle rangewithin the aperture 263 e. This means that the input friction plate 263is movable through a predetermined angle range with respect to the firstand second low-friction-coefficient friction washers 262 and 264. Morespecifically, a rotating-direction space 246 of a torsion angle of θ1 isensured on the forward side, in the rotational direction R2, of thefirst projected portion 264 a, and a rotating-direction space 247 of atorsion angle of θ2 is formed on the forward side, in the rotationaldirection R1, of the first projected portion 264 a. Consequently, thetotal torsion angle, i.e., the sum of the torsion angles of θ1 and θ2provides the predetermined angle, by which the first and secondlow-friction-coefficient friction washers 262 and 264 can rotaterelatively to the input friction plate 263. In this embodiment, thetotal torsion angle is equal to 8° (see FIG. 42). This total torsionangle is preferably in a range slightly exceeding a damper operationangle, which is caused by minute torsional vibrations due to combustionvariations of the engine.

[0273] As seen in FIG. 49, the engagement between the second projectedportions 264 b of the second low-friction-coefficient friction washer264 and the apertures 271 a in the first high-friction-coefficientfriction washer 261 as well as the engagement between the projectedportions 273 a of the second high-friction-coefficient friction washer265 and the concavities 264 c in the second low-friction-coefficientfriction washer 264 form a second rotating-direction engagement portion282. The relationship between the projected portions and the concavitiesforming the former engagement is the same or substantially the same asthat in the latter engagement, therefore, the following description willbe given on only the engagement between the second projected portions264 b of the second low-friction-coefficient friction washer 264 and theapertures 271 a in the first high-friction-coefficient friction washer261 for the sake of simplifying.

[0274] In the second rotating-direction engagement portion 282, thecircumferential width of the second projected portion 264 b is shorterthan that of the aperture 271 a, therefore, the second projected portion264 b can move through a predetermined angle range within the aperture271 a. This means that the first and second low-friction-coefficientfriction washers 262 and 264 are movable through a predetermined anglerange with respect to the first and second high-friction-coefficientfriction washers 261 and 265. More specifically, a rotating-directionspace 285 of a torsion angle of θ3 is ensured on the forward side, inthe rotational direction R2, of the second projected portion 264 b, anda rotating-direction space 286 of a torsion angle of θ4 is formed on theforward side, in the rotational direction R1, of the second projectedportion 264 b. Consequently, the total torsion angle, i.e., the sum ofthe torsion angles of θ3 and θ4 provides the predetermined angle, bywhich the first and second low-friction-coefficient friction washers 262and 264 can rotate relatively to the first and secondhigh-friction-coefficient friction washers 261 and 265. In thisembodiment, the total torsion angle is equal to 2° (see FIG. 42).

[0275] As seen in FIGS. 46 and 47, the frictional resistance generatingmechanism 207 further includes a bushing 266. The bushing 266 is formedof a plurality of members to support radially the respective washerswith respect to the inner cylindrical portion 228, and is disposedradially between the inner peripheries of the washers and the innercylindrical portion 228. The bushing 266 has a predetermined axiallength, and each portion thereof has an arc-shaped form when viewed inthe axial direction. The bushing 266 has a smooth peripheral surface,which is rotatably supported by an outer peripheral surface 228 b of thefree end portion of the inner cylindrical portion 228.

[0276] In the frictional resistance generating mechanism 207 describedabove, the engagement between the first low friction-coefficientfriction washer 262 and the core plate 271 of the firsthigh-friction-coefficient friction washer 261 as well as the engagementbetween the second low-friction-coefficient friction washer 264 and thecore plate 273 of the second high-friction-coefficient friction washer265 provides a first frictional resistance generating portion 288.Further, a second frictional resistance generating portion 289 isprovided by the engagement between the first high-friction-coefficientfriction washer 261 and the output friction plate 244 as well as theengagement between the second high-friction-coefficient friction washer265 and the flywheel 221 having the friction surface.

[0277] (3-2) Operation of Frictional Resistance Generating Mechanism

[0278] As seen in FIG. 51, when the clutch device 1 receives thecombustion variations from the engine, the damper mechanism 206 operatesto rotate the input disk-shaped plate 232 relatively to the outputdisk-shaped plates 230 and 231 so that the plurality of coil springs 233and others are compressed are compressed between them. Further, thefrictional resistance generating mechanism 207 generates a predeterminedhysteresis torque. Through the foregoing operations, the torsionalvibrations are absorbed and damped. More specifically, the coil springs233 are compressed between the circumferential ends of the windowapertures in the input disk-shaped plate 232 and the circumferentialends of the windows in the output disk-shaped plates 230 and 231.

[0279] In the frictional resistance generating mechanism 207, the firstand second high-friction-coefficient friction washers 261 and 265 rotatetogether with input friction plate 263 with the first and secondlow-friction-coefficient friction washers 262 and 264 therebetween, androtate relatively to the output friction plate 244 and the flywheel 221having the friction surface. Consequently, sliding occurs between theoutput friction plate 244 and the first high-friction-coefficientfriction washer 261, and also occurs between the secondhigh-friction-coefficient friction washer 265 and the flywheel 221having the friction surface. Thus, the second frictional resistancegenerating mechanism 289 operates to generate a relatively largefrictional resistance.

[0280] (3-2-1) Minute Torsional Vibrations

[0281] Description will now be given on the operation of the dampermechanism 206, which is performed when minute torsional vibrations dueto the combustion variations of the engine are applied to the clutchdevice 1, with reference to a mechanical circuit diagram of FIG. 51 anda torsion characteristic diagram of FIG. 42. When minute torsionalvibrations are applied to the damper mechanism 206, in which the coilsprings 233 are in the compressed state, the first and secondlow-friction-coefficient friction washers 262 and 264 of the frictionalresistance generating mechanism 207 rotate in the minuterotating-direction space (246 and 247), which is defined in the aperture263 e of the input friction plate 263 by the first projected portion 264a of the second low-friction-coefficient friction washer 264, and thusrotates relatively the input friction plate 263. Thus, input frictionplate 263 does not drive the first and second low-friction-coefficientfriction washers 262 and 264, therefore, neither of the first and secondfrictional resistance generating portions 288 and 289 generate africtional resistance (see FIG. 43). Consequently, a high hysteresistorque does not occur in response to the minute torsional vibrations.For example, in “AC2 HYS” illustrated in the torsion characteristicdiagram of FIG. 42, the coil springs 233 operate, but no sliding occursin the frictional resistance generating mechanism 207. In thepredetermined torsion angle range, only a hysteresis torque, which ismuch smaller than an ordinary hysteresis torque, can be obtained. Asdescribed above, the structure employs the minute rotating-directionspace (246 and 247), which does not operate the frictional resistancegenerating mechanism 207 within a predetermined angle range in thetorsion characteristics. Therefore, the levels of the vibrations andnoises can be significantly reduced.

[0282] When the torsion angle of the minute torsional vibrations exceedsthe angle of the first rotating-direction engagement portion 281, therotating-direction space (246 and 247) disappears in the firstrotating-direction engagement portion 281 and the input friction plate263 drives the first and second low-friction-coefficient frictionwashers 262 and 264 in the rotational direction. Consequently, the firstand second low-friction-coefficient friction washers 262 and 264 rotaterelatively to the first and second high-friction-coefficient frictionwashers 261 and 265. Thus, the first frictional resistance generatingportion 288 operates to generate a relatively small frictionalresistance (see FIG. 44).

[0283] When the torsion angle of the torsional vibrations furtherincreases, the circumferential space (285 and 286) in the secondrotating-direction engagement portion 282 disappears, and then the firstand second low-friction-coefficient friction washers 262 and 264 drivethe first and second high-friction-coefficient friction washers 261 and265 in the rotational direction. Thereby, the first and secondhigh-friction-coefficient friction washers 261 and 265 rotate relativelyto the output friction plate 244 and the flywheel 221 having thefriction surface. Thus, the second frictional resistance generatingportion 289 operates to generate a relatively large frictionalresistance (see FIG. 45).

[0284] (3-2-2) Large-Angle Torsional Vibrations

[0285] As already described, when the torsion angle of the torsionalvibrations is large, sliding occurs between the output friction plate244 and the first high-friction-coefficient friction washer 261 andsliding also occurs between the second high-friction-coefficientfriction washer 265 and the flywheel 221 having the friction surface.

[0286] At an end of the torsion angle range (i.e., the position wherethe direction of the vibration changes), operations are performed asfollows. On the right end in the torsion characteristic diagram of FIG.42, the first and second low-friction-coefficient friction washers 262and 264 are in the positions shifted in the rotational direction R2 tothe maximum extent with respect to the input friction plate 263, and thefirst and second high-friction-coefficient friction washers 261 and 265are in the positions shifted in the rotational direction R2 to themaximum extent with respect to the first and secondlow-friction-coefficient friction washers 262 and 264. When the inputfriction plate 263 rotates relatively to the flywheel 221 having thefriction surface in the rotational direction R2, the input frictionplate 263 angularly moves throughout the rotating-direction space (246and 247) of the first rotating-direction engagement portion 281 androtates relatively to the first and second low-friction-coefficientfriction washers 262 and 264. During this operation, neither of thefirst and second frictional resistance generating portions 288 and 289generates the frictional resistance. When the rotating-direction space(246 and 247) in the first rotating-direction engagement portion 281disappears, the first and second low-friction-coefficient frictionwashers 262 and 264 drive the first and second high-friction-coefficientfriction washers 261 and 265. Thereby, the first and secondlow-friction-coefficient friction washers 262 and 264 angularly movethroughout the rotating-direction space (285 and 286) in the secondrotating-direction engagement portion 282, and rotate relatively to thefirst and second high-friction-coefficient friction washers 261 and 265.During this operation, the first frictional resistance generatingportion 288 operates to generate a relatively small frictionalresistance.

[0287] When the rotating-direction space (285 and 286) in the secondrotating-direction engagement portions 282 disappears, the first andsecond low-friction-coefficient friction washers 262 and 264 drive thefirst and second high-friction-coefficient friction washers 261 and 265.Thereby, the first and second high-friction-coefficient friction washers261 and 265 rotate relatively to the output friction plate 244 and theflywheel 221 having the friction surface. Thereby, the second frictionalresistance generating portion 289 operates to generate a largefrictional resistance.

[0288] As described above, the first frictional resistance generatingportion 288 generates a frictional resistance of an intermediatemagnitude within the torsion angle range of the rotating-direction space(285 and 286) in the second rotating-direction engagement portion 282before the second frictional resistance generating portion 289 operatesto generate a large frictional resistance. As described above, the largefrictional resistance rises in a multi-step or stepwise fashion so thata wall of a high hysteresis torque does not exist when generating thelarge frictional resistance. Thereby, hitting or tapping noises ofclaws, which may occur when a high hysteresis torque occurs, can bereduced in the frictional resistance generating mechanism, which isprovided with the minute space in the rotational direction for absorbingthe minute torsional vibrations.

[0289] In the frictional resistance generating mechanism 207, therotating-direction space (246 and 247) in the first rotating-directionengagement portion 281 is not located radially outside an area, in whichthe first and second low-friction-coefficient friction washers 262 and264 axially overlap with the first and second high-friction-coefficientfriction washers 261 and 265. Therefore, the whole structure can berelatively compact.

[0290] In this frictional resistance generating mechanism 207, therotating-direction space (246 and 247) in the first rotating-directionengagement portion 281 is formed between the secondlow-friction-coefficient friction washer 264 and the disk-shaped portion263 a of the input friction plate 263. Therefore the structure providingthe rotating-direction space (246 and 247) becomes simpler. Thisimproves the accuracy of the rotating-direction space.

[0291] Fourth Embodiment

[0292] Referring to a mechanical circuit diagram of FIG. 52, descriptionwill now be given on a frictional resistance generating mechanism 307 inthe fourth embodiment.

[0293] The frictional resistance generating mechanism 307 includes afirst rotary member 363, a second rotary member 330, a firstintermediate member 362, and a second intermediate member 372. The firstand second rotary members 363 and 330 are rotatable relatively to eachother, and are coupled together in the rotational direction by elasticmembers (not shown). The first and second intermediate members 362 and372 are disposed between the first and second rotary members 363 and 330to operate in series in the rotational direction. The first intermediatemember 362 is engaged with the first rotary member 363 via a firstrotating-direction space forming portion 381 and is further engaged withthe second intermediate member 372 via a second rotating-direction spaceforming portion 382. The first intermediate member 362 is frictionallyengaged with the second rotary member 330 via a first frictiongenerating portion 388. The second intermediate member 372 isfrictionally engaged with the second rotary member 330 via a secondfriction generating portion 389. As described above, the first andsecond friction generating portions 388 and 389 are disposedcircumferentially between the first and second rotary members 363 and330 to operate in parallel with each other.

[0294] Referring to the mechanical circuit diagram of FIG. 52 and atorsion characteristic diagram of FIG. 53, description will now be givenon an operation of this frictional resistance generating mechanism 307,in which the first rotary member 363 rotates relatively to the secondrotary member 330.

[0295] In an initial torsion stage, neither of the first and secondfriction generating portions 388 and 389 operates owing to therotating-direction space in the first rotating-direction space formingportion 381. This provides a region, where a hysteresis torque hardlyoccurs.

[0296] When the rotating-direction space in the first rotating-directionspace forming portion 381 disappears, the first rotary member 363 startsto drive the first intermediate member 362 in the rotational direction.In this operation, the first friction generating portion 388 operates togenerate a predetermined frictional resistance (DC1 in FIG. 53). In thisoperation, the second friction generating portion 389 does not operateowing to the second rotating-direction space forming portion 382.

[0297] When the rotating-direction space in the secondrotating-direction space forming portion 382 disappears, the firstintermediate member 362 drives the second intermediate member 372 in therotational direction. In this operation, the second friction generatingportion 389 operates to generate a predetermined frictional resistance(DC2 in FIG. 53). During this operation, the first friction generatingportion 388 is also operating so that a frictional resistance producedin this state is larger than that produced when only the first frictiongenerating portion 388 is operating.

[0298] As described above, the large frictional resistance rises in amulti-step or stepwise fashion so that a wall of a high hysteresistorque does not exist when generating the large frictional resistance.Thereby, hitting or tapping noises of claws, which may occur when a highhysteresis torque occurs, can be reduced in the frictional resistancegenerating mechanism.

[0299] Referring to a mechanical circuit diagram of FIG. 54, descriptionwill now be given on a frictional resistance generating mechanism 307′in a fifth embodiment.

[0300] The frictional resistance generating mechanism 307′ includes thefirst rotary member 363, the second rotary member 330, the firstintermediate member 362, a second intermediate member 372′, and a thirdintermediate member 385. The first and second rotary members 363 and 330are rotatable relatively to each other and are coupled together in therotational direction by elastic members (not shown). The first, secondand third intermediate members 362, 372′, and 385 are disposed betweenthe first and second rotary members 363 and 330 to operate in series inthe rotational direction. The first intermediate member 362 is engagedwith the first rotary member 363 via the first rotating-direction spaceforming portion 381, and is engaged with the second intermediate member372′ via the second rotating-direction space forming portion 382. Thesecond intermediate member 372′ is engaged with the third intermediatemember 385 via a third rotating-direction space forming portion 383. Thefirst intermediate member 362 is frictionally engaged with the secondrotary member 330 via the first friction generating portion 388. Thesecond intermediate member 372′ is frictionally engaged with the secondrotary member 330 via the second friction generating portion 389. Thethird intermediate member 385 is frictionally engaged with the secondrotary member 330 via a third friction generating portion 390. Asdescribed above, the first, second and third friction generatingportions 388, 389, and 390 are disposed circumferentially between thefirst and second rotary members 363 and 330 to operate in parallel witheach other.

[0301] Referring to the mechanical circuit diagram of FIG. 54 and atorsion characteristic diagram of FIG. 55, description will now be givenon an operation of this frictional resistance generating mechanism 307′,in which the first rotary member 363 rotates relatively to the secondrotary member 330.

[0302] In an initial torsion stage, any one of the first, second andthird friction generating portions 388, 389, and 390 does not operateowing to the rotating-direction space in the first rotating-directionspace forming portion 381. This provides a region, where a hysteresistorque hardly occurs.

[0303] When the rotating-direction space in the first rotating-directionspace forming portion 381 disappears, the first rotary member 363 startsto drive the first intermediate member 362 in the rotational direction.In this operation, the first friction generating portion 388 operates togenerate a predetermined frictional resistance (DC1 in FIG. 55). In thisoperation, the second friction generating portion 389 does not operateowing to the second rotating-direction space forming portion 382, andthe third friction generating portion 390 does not operate owing to thethird rotating-direction space forming portion 383.

[0304] When the rotating-direction space in the secondrotating-direction space forming portion 382 disappears, the firstintermediate member 362 drives the second intermediate member 372′ inthe rotational direction. In this operation, the second frictiongenerating portion 389 operates to generate a predetermined frictionalresistance (DC2 in FIG. 55). During this operation, the first frictiongenerating portion 388 is also operating so that both the frictiongenerating portions produce a frictional resistance larger than that,which is produced when only the first friction generating portion 388 isoperating. In this operation, the third friction generating portion 390does not operate owing to the third rotating-direction space formingportion 383.

[0305] When the rotating-direction space in the third rotating-directionspace forming portion 383 disappears, the second intermediate member372′ drives the third intermediate member 385 in the rotationaldirection. In this operation, the third friction generating portion 390operates to generate a predetermined frictional resistance (DC3 in FIG.55). During this operation, the first and second friction generatingportions 388 and 389 are also operating so that the friction generatingportions produce a frictional resistance larger than that which isproduced when only the first and second friction generating portions 388and 389 are operating.

[0306] In this embodiment, since the large frictional resistance occursthrough three stages, the wall of the large hysteresis torque, which mayoccur when generating the large frictional resistance, can be furthersmall so that hitting or tapping noises of claws can be further reducedin the frictional resistance generating mechanism when generating thehigh hysteresis torque.

[0307] The large frictional resistance may be configured to rise throughfour or more stages.

[0308] Sixth Embodiment

[0309] As illustrated in FIG. 56, the large frictional resistance may beraised smoothly instead of a multi-step fashion. In other words, anintermediate frictional resistance may be raised gradually beforegenerating a large frictional resistance. In FIG. 56, a solid linerepresents a linear change in intermediate frictional resistance.Further, broken lines in FIG. 56 represent a manner, in which anincreasing rate of the torque with respect to the angle decreases withangle, and a manner, in which the above rate increases with angle.

[0310] Other Embodiments

[0311] Although the embodiments of the clutch devices according to thepresent invention have been described and illustrated in detail, theinvention is not restricted to such embodiments and can be variouslymodified or changed without departing from the scope of the invention.

[0312] In the damper mechanism according to the invention, therotating-direction space in the frictional resistance suppressingmechanism prevents the operation of the frictional resistance generatingmechanism in both the ranges of small and large torsion angles of minutetorsional vibrations. Thus, a large frictional resistance does not occurin response to minute torsional vibrations in the first stage of thetorsion characteristics so that torsional vibration damping performancesare improved.

Effect of the Invention

[0313] In the frictional resistance generating mechanism according tothe present invention, when the torsion angle of the torsionalvibrations is within the angle range of the first rotating-directionspace in the first frictional resistance suppressing portion, the firstrotating-direction space prevents the operations of the first and secondfrictional resistance generating portions so that a large frictionalresistance does not occur. When the torsion angle of the torsionalvibrations is within the angle range of the second rotating-directionspace of the second frictional resistance suppressing portion, thesecond rotating-direction space operates only the first frictionalresistance generating portion to generate a frictional resistance of anintermediate magnitude. When the torsion angle of the torsionalvibrations exceeds the angle range of the second rotating-directionspace, the second frictional resistance generating portion operates togenerate the largest frictional resistance.

[0314] As described above, the first frictional resistance generatingportion generates the frictional resistance of an intermediate magnitudein the torsion angle range of the second rotating-direction space beforethe second frictional resistance generating portion operates to generatethe large frictional resistance. In this manner, the large frictionalresistance rises in a multi-step or stepwise fashion so that a wall of ahigh hysteresis torque does not exist when the large frictionalresistance is generated. Thereby, hitting or tapping noises of claws,which may occur when a high hysteresis torque occurs, can be reduced inthe frictional resistance generating mechanism

[0315] In the flywheel assembly according to the invention, theplate-like coupling portion is radially shorter than the conventionalstop pin, and therefore can be arranged in the radially outermostposition of the second disk-shaped plate. Accordingly, the plate-likecoupling portion does not interfere with the elastic member so that thetorsion angle of the damper mechanism can be sufficiently increased.

[0316] As used herein, the following directional terms “forward,rearward, above, downward, vertical, horizontal, below, and transverse”as well as any other similar directional terms refer to those directionsof a vehicle equipped with the present invention. Accordingly, theseterms, as utilized to describe the present invention should beinterpreted relative to a vehicle equipped with the present invention.

[0317] Terms that are expressed as “means-plus function” in the claimsshould include any structure that can be utilized to carry out thefunction of that part of the present invention.

[0318] The terms of degree such as “substantially,” “about,” and“approximately” as used herein mean a reasonable amount of deviation ofthe modified term such that the end result is not significantly changed.For example, these terms can be construed as including a deviation of atleast ±5% of the modified term if this deviation would not negate themeaning of the word it modifies.

[0319] This application claims priority to Japanese Patent ApplicationsNos. 2002307250, 2002-307251, 2002-351589, and 2003-162896. The entiredisclosures of Japanese Patent Application Applications Nos.2002-307250, 2002-307251, 2002-351589, and 2003-162896 are herebyincorporated herein by reference.

[0320] While only selected embodiments have been chosen to illustratethe present invention, it will be apparent to those skilled in the artfrom this disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents. Thus, the scope ofthe invention is not limited to the disclosed embodiments.

What is claimed is:
 1. A damper mechanism for transmitting a torquewhile absorbing and damping torsional vibrations, comprising: a firstrotary member; a second rotary member being rotatable relatively to saidfirst rotary member; a first elastic member being arranged to becompressed in response to relative rotation between said first andsecond rotary members; a second elastic member being compressed inresponse to relative rotation between said first and second rotarymembers, said second elastic member having a higher rigidity than saidfirst elastic member; a frictional resistance generating mechanism beingconfigured to generate a frictional resistance when said first elasticmember is in a compressed state and when said second elastic member isin a compressed state; and a frictional resistance suppressing mechanismhaving a rotating-direction space to prevent an operation of saidfrictional resistance generating mechanism in a predetermined anglerange.
 2. The damper mechanism according to claim 1, wherein saidfrictional resistance generating mechanism and said frictionalresistance suppressing mechanism are arranged to operate in parallelwith said first and second elastic members in a rotational direction. 3.The damper mechanism according to claim 2, wherein said first and secondelastic members are arranged to operate in series in said rotationaldirection.
 4. The damper mechanism according to claim 3, wherein saidfrictional resistance generating mechanism operates in first regions toincrease stepwise frictional resistance on opposite sides of a range ofa predetermined angle, respectively, and a second region to provide aconstant frictional resistance.
 5. The damper mechanism according toclaim 4, wherein said frictional resistance generating mechanismgenerates an intermediate frictional resistance in said first region,said intermediate frictional resistance is greater than a low frictionalresistance and less than a high frictional resistance said frictionalresistance generating mechanism generates.
 6. The damper mechanismaccording to claim 4, wherein said frictional resistance generatingmechanism generates a frictional resistance increasing smoothly in saidfirst region.
 7. The damper mechanism according to claim 2, wherein saidfrictional resistance generating mechanism operates in first regions toincrease stepwise frictional resistance on opposite sides of a range ofa predetermined angle, respectively, and a second region to provide aconstant frictional resistance.
 8. The damper mechanism according toclaim 7, wherein said frictional resistance generating mechanismgenerates an intermediate frictional resistance in said first region,said intermediate frictional resistance is greater than a low frictionalresistance and less than a high frictional resistance said frictionalresistance generating mechanism generates.
 9. The damper mechanismaccording to claim 8, wherein said frictional resistance generatingmechanism generates a frictional resistance increasing smoothly in saidfirst region.
 10. The damper mechanism according to claim 1, whereinsaid frictional resistance generating mechanism operates in firstregions to increase stepwise frictional resistance on opposite sides ofa range of a predetermined angle, respectively, and a second region toprovide a constant frictional resistance.
 11. The damper mechanismaccording to claim 10, wherein said frictional resistance generatingmechanism generates an intermediate frictional resistance in said firstregion, said intermediate frictional resistance is greater than a lowfrictional resistance and less than a high frictional resistance saidfrictional resistance generating mechanism generates.
 12. The dampermechanism according to claim 11, wherein said frictional resistancegenerating mechanism generates a frictional resistance increasingsmoothly in said first region.
 13. A frictional resistance generatingmechanism arranged between two relatively rotatable members of a rotarymechanism for generating a frictional resistance in response to relativerotation occurring between the two members by torsional vibrations todamp the torsional vibrations, said frictional resistance generatingmechanism comprising: a first frictional resistance generating portion;a second frictional resistance generating portion generating africtional resistance larger than that generated by said firstfrictional resistance generating portion; a first frictional resistancesuppressing portion having a first rotating-direction space to preventoperation of both of said first and second frictional resistancegenerating portions; and a second frictional resistance suppressingportion having a second rotating-direction space to prevent operation ofonly said second frictional resistance generating portion on oppositesides of a torsion angle range of said first rotating-direction space.14. A frictional resistance generating mechanism arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation occurring betweenthe two members by torsional vibrations to damp the torsionalvibrations, said frictional resistance generating mechanism comprising:a first frictional resistance generating portion being inoperable in afirst torsion angle range and operable in second torsion angle rangesprovided on opposite sides of said first torsion angle range,respectively; and a second frictional resistance generating portionbeing inoperable in said first and second torsion angle ranges andoperable on opposite sides of said second torsion angle ranges.
 15. Africtional resistance generating mechanism arranged between tworelatively rotatable members of a rotary mechanism for generating africtional resistance in response to relative rotation occurring betweenthe two members by torsional vibrations to damp the torsionalvibrations, said frictional resistance generating mechanism comprising:a large frictional resistance generating mechanism being configured togenerate a large frictional resistance; a large frictional resistancegeneration suppressing mechanism having a rotating-direction space toprevent operation of said large frictional resistance generatingmechanism; and a small frictional resistance generating mechanism beingconfigured to generate a frictional resistance being smaller than saidlarge frictional resistance generated by said large frictionalresistance generating mechanism on opposite sides of saidrotating-direction space.
 16. A frictional resistance generatingmechanism arranged between two relatively rotatable members of a rotarymechanism for generating a frictional resistance in response to relativerotation occurring between the two members by torsional vibrations todamp the torsional vibrations, said frictional resistance generatingmechanism comprising: a first friction portion having, a firsthysteresis torque generating portion being configured to generate afirst hysteresis torque, and a first rotating-direction space arrangedto operate in series with respect to said first hysteresis torquegenerating portion in a rotating direction; and a second frictionportion arranged in said rotating direction and between said firsthysteresis torque generating portion and said first rotating-directionspace having a second hysteresis torque generating portion generating asecond hysteresis torque smaller than said first hysteresis torque, anda second rotating-direction space being arranged to operate in serieswith respect to said second hysteresis torque generating portion in saidrotating direction.
 17. A frictional resistance generating mechanismarranged between two relatively rotatable members of a rotary mechanismfor generating a frictional resistance in response to relative rotationoccurring between the two members by torsional vibrations to damp thetorsional vibrations, said frictional resistance generating mechanismcomprising: a first friction generating portion; a second frictiongenerating portion arranged to operate in parallel with said firstfriction generating portion in the rotating direction; a firstrotating-direction space forming portion being configured to preventoperation of said first friction generating portion in an initial stageof a torsion angle; and a second rotating-direction space formingportion being configured to prevent operation of said second frictiongenerating portion up to a predetermined torsion angle when said firstfriction generating portion is operating.
 18. A frictional resistancegenerating mechanism arranged between two relatively rotatable membersof a rotary mechanism for generating a frictional resistance in responseto relative rotation occurring between the two members by torsionalvibrations to damp the torsional vibrations, said frictional resistancegenerating mechanism comprising: first, second, and third frictiongenerating portions arranged to operate in parallel with each other in arotating direction between said first and second rotary members; a firstrotating-direction space forming portion being configured to preventoperation of said first friction generating portion in an initial stageof a torsion angle; a second rotating-direction space forming portionbeing configured to prevent operation of said second friction generatingportion up to a predetermined torsion angle when said first frictiongenerating portion is operating; and a third rotating-direction spaceforming portion being configured to prevent operation of said thirdfriction generating portion up to a predetermined torsion angle whensaid second friction generating portion is operating.
 19. A frictionalresistance generating mechanism arranged between two relativelyrotatable members of a rotary mechanism for generating a frictionalresistance in response to relative rotation occurring between the twomembers by torsional vibrations to damp the torsional vibrations, saidfrictional resistance generating mechanism comprising: a plurality offriction generating portions being arranged between said first andsecond rotary members to operate in parallel with each other in therotating direction; and a plurality of rotating-direction space formingportions being configured to delay operation of said plurality offriction portions enabling said respective friction portions to startoperating successively.
 20. A frictional resistance generating mechanismarranged between two relatively rotatable members of a rotary mechanismfor generating a frictional resistance in response to relative rotationoccurring between the two members by torsional vibrations to damptorsional vibrations, said frictional resistance generating mechanismcomprising: a large friction generating portion; and an intermediatefriction generating portion generating an intermediate frictionalresistance smaller than a frictional resistance generated by said largefrictional resistance generating portion before said large frictiongenerating portion starts operating.
 21. A flywheel assembly fortransmitting a torque from a crankshaft of an engine, comprising: aflywheel having a friction surface; an elastic coupling mechanism beingconfigured to couple elastically said flywheel and the crankshaft in arotating direction, and having a pair of first disk-shaped members beingaxially spaced from each other and fixed together, a second disk-shapedmember being arranged between said pair of first disk-shaped members,and an elastic member to couple elastically said first disk-shapedmembers to said second disk-shaped member in said rotating direction;and a plate-like coupling portion extending between outer peripheries ofsaid paired first disk-shaped members, and fixing said pair of firstdisk-shaped members together.
 22. The flywheel assembly according toclaim 1, wherein said plate-like coupling portions are arranged at aplurality of circumferentially shifted positions, respectively.
 23. Theflywheel assembly according to claim 22, wherein said plate-likecoupling portion has main surfaces directed radially inward and outward,respectively.
 24. The flywheel assembly according to claim 23, whereinsaid plate-like coupling portion extends integrally from one of saidpair of first disk-shaped members.
 25. The flywheel assembly accordingto claim 24, wherein said second disk-shaped member is provided with astop portion that is arranged to collide in the rotational directionwith said disk-shaped member when a torsion angle etween said firstdisk-shaped member pair and said second disk-shaped member increases.26. The flywheel assembly according to claim 21, wherein said plate-likecoupling portion has main surfaces directed radially inward and outward,respectively.
 27. The flywheel assembly according to claim 21, whereinsaid plate-like coupling portion extends integrally from one of saidpair of first disk-shaped members.
 28. The flywheel assembly accordingto claim 27, wherein said second disk-shaped member is provided with astop portion that is arranged to collide in the rotational directionwith said disk-shaped member when a torsion angle between said firstdisk-shaped member pair and said second disk-shaped member increases.29. The flywheel assembly according to claim 21, wherein said seconddisk-shaped member is provided with a stop portion that is arranged tocollide in the rotational direction with said disk-shaped member when atorsion angle between said first disk-shaped member pair and said seconddisk-shaped member increases.
 30. A frictional resistance generatingmechanism arranged between two relatively rotatable members of a rotarymechanism for generating a frictional resistance in response to relativerotation occurring between the two members by torsional vibrations todamp the torsional vibrations, said frictional resistance generatingmechanism comprising: a first rotary member; a second rotary memberbeing rotatable relatively to said first rotary member; a firstintermediate member engaging with said first rotary member via a firstrotating-direction space; and a second intermediate member cooperatingwith said first intermediate member to form an engagement portionengaging with said first intermediate member via a secondrotating-direction space, cooperating with said first intermediatemember to form a first frictional resistance generating portion slidablyand frictionally engaging in a rotating direction with said firstintermediate member, and cooperating with said second rotary member toform a second frictional resistance generating portion slidably andfrictionally engaging in said rotating direction with said second rotarymember to generate a frictional resistance larger than a frictionalresistance generated by said first frictional resistance generatingportion.
 31. The frictional resistance generating mechanism according toclaim 30, wherein said first rotating-direction space is larger thansaid second rotating-direction space.
 32. The frictional resistancegenerating mechanism according to claim 31, wherein said first andsecond intermediate members are disk-shaped members axially overlappingand being in contact with each other.
 33. The frictional resistancegenerating mechanism according to claim 32, wherein said secondintermediate member is formed of a pair of members each being in contactwith one of axially opposite sides of said first intermediate member,and each of said pair of members cooperates with said first intermediatemember to form said first frictional resistance generating portiontherebetween, and cooperates with said second rotary member to form saidsecond frictional resistance generating portion therebetween.
 34. Thefrictional resistance generating mechanism according to claim 33,wherein said first rotating-direction space is radially positioned in anarea including axially overlapping portions of said first and secondintermediate members.
 35. The frictional resistance generating mechanismaccording to claim 34, wherein said first rotary member has adisk-shaped portion axially overlapping said first intermediate member,and said first rotating-direction space is formed between said firstintermediate member and said disk-shaped portion of said first rotarymember.
 36. The frictional resistance generating mechanism according toclaim 35, wherein one of said first intermediate member and saiddisk-shaped portion of said first rotary member is provided with a spaceextending in the rotating direction, and the other is provided with aprojected portion extending axially through said space to form saidfirst rotating-direction space.
 37. The frictional resistance generatingmechanism according to claim 36, wherein said space is formed in saiddisk-shaped portion of said first rotary member, said first intermediatemember is formed of a pair of members arranged on axially opposite sidesof said disk-shaped portion, respectively, and one of said pair ofmembers has said projected portion, and is unrotatably engaged with theother of said pair of member via said projected portion.
 38. Thefrictional resistance generating mechanism according to claim 30,wherein said first and second intermediate members are disk-shapedmembers axially overlapping and being in contact with each other. 39.The frictional resistance generating mechanism according to claim 38,wherein said second intermediate member is formed of a pair of memberseach being in contact with one of axially opposite sides of said firstintermediate member, and each of said pair of members cooperates withsaid first intermediate member to form said first frictional resistancegenerating portion therebetween, and cooperates with said second rotarymember to form said second frictional resistance generating portiontherebetween.
 40. The frictional resistance generating mechanismaccording to claim 38, wherein said first rotating-direction space isradially positioned in an area including axially overlapping portions ofsaid first and second intermediate members.
 41. The frictionalresistance generating mechanism according to claim 40, wherein saidfirst rotary member has a disk-shaped portion axially overlapping saidfirst intermediate member, and said first rotating-direction space isformed between said first intermediate member and said disk-shapedportion of said first rotary member.
 42. The frictional resistancegenerating mechanism according to claim 41, wherein one of said firstintermediate member and said disk-shaped portion of said first rotarymember is provided with a space extending in the rotating direction, andthe other is provided with a projected portion extending axially throughsaid space to form said first rotating-direction space.
 43. Thefrictional resistance generating mechanism according to claim 42,wherein said space is formed in said disk-shaped portion of said firstrotary member, said first intermediate member is formed of a pair ofmembers arranged on axially opposite sides of said disk-shaped portion,respectively, and one of said pair of members has said projectedportion, and is unrotatably engaged with the other of said pair ofmember via said projected portion.
 44. A frictional resistancegenerating mechanism arranged between two relatively rotatable membersof a rotary mechanism for generating a frictional resistance in responseto relative rotation occurring between the two members by torsionalvibrations to damp the torsional vibrations, said frictional resistancegenerating mechanism comprising: a first rotary member; a second rotarymember being rotatable relatively to said first rotary member; a firstintermediate member engaging with said first rotary member via a spacein the first rotating-direction, and cooperating with said second rotarymember to form a first friction generating portion therebetween; and asecond intermediate member being arranged between said first and secondrotary members to operate with respect to said first intermediate memberin a rotating direction such that an end of said second intermediatemember and an end of said first intermediate member exert forces on eachother, engaging with said first intermediate member via a second spacein the rotating-direction, and cooperating with said second rotarymember to form a second friction generating portion therebetween. 45.The frictional resistance generating mechanism according to claim 44,further comprising: a third intermediate member arranged between saidfirst and second rotary members to operate with respect to said firstand second intermediate members in the rotating direction such that anend of said third intermediate member and an end of said first andsecond intermediate members exert forces on each other, engaging withsaid second intermediate member via a third rotating-direction space,and cooperating with said second rotary member to form a third frictiongenerating portion.
 46. A frictional resistance generating mechanismarranged between two relatively rotatable members of a rotary mechanismfor generating a frictional resistance in response to relative rotationoccurring between the two members by torsional vibrations to damp thetorsional vibrations, said frictional resistance generating mechanismcomprising: a first rotary member; a second rotary member beingrotatable relatively to said first rotary member; and a plurality offriction members arranged in a rotating direction between said first andsecond rotary members, each frictionally engaging with said secondrotary member, and engaging with each other in the rotating directionvia a rotating-direction space such that an end of one exerts force onan end of the other.